Could not load file or assembly ... An attempt was made to load a program with an incorrect format (System.BadImageFormatException)

I am pretty sure you're having a 32-bit / 64-bit conflict. It sounds like your main project might be set to 32-bit while the class its referencing is set to 64-bit. Try looking at this SO question and this one too. Between the two of them, you should be able to figure out your problem.

---

Might be you are facing the problem with your website after deploying on server.

Then you need to adjust your application pool to Enable 32-Bit Applications.

Steps

Open IIS Manager Click on Application Pools Select whatever application pool you are using From right pane, click Advanced Settings... Set Enable 32-Bit Applications to True

---

I just had this error message running IIS Express in Visual Studio 2015. In my case I needed to be running the 64 bit version of IIS Express:

Tools → Options → Projects and Solutions → Web Projects Check the box that says "Use the 64 bit version of IIS Express for web sites and projects".

Screenshot:

https://i.stack.imgur.com/1EG2c.png

---

I had this same problem. I had set Project A's "Platform Target" ("Project A"(Right Click)->Properties->Build->"Platform Target") to x86 but kept Project B's at "Any CPU". Setting Project B's to "x86" fixed this.

---

I had this problem running unit tests (xunit) in Visual Studio 2015 and came across the following fix:

Menu Bar -> Test -> Test Settings -> Default Processor Architecture -> X64

---

You may need to change the Appication Pool setting "Enable 32bit Applications" to TRUE in IIS7 if you have at least 1 32bit dll\exe in your project.

---

First of all I got this in VS2017 with an old project I needed to make a tiny change to and upraded all the projects to framework 4.7.

Several others have mentioned selecting Any CPU can fix this issue.

There's a couple places you need to do it, and it might not just be as simple as selecting from the dropdown. This fixed it for me:

1) You need to do it both here:

https://i.stack.imgur.com/M0uoe.png

2) And also in Configuration Manager (right click on solution)

https://i.stack.imgur.com/ytrVE.png

But what if it isn't there???

Then click New and choose these settings: (thanks @RckLN)

https://i.stack.imgur.com/yetiy.png

---

https://i.stack.imgur.com/oD44Q.png

---

https://i.stack.imgur.com/jBG0u.png

---

I had the same issue with multiple projects in the same solution, i ended up setting all of the target frameworks to .NET Framework 4 and x86 for the target CPU and it finally successfully compiled.

---

None of these solutions worked for me - but by deleting the contents of bin and obj folders everything was cool again.

---

I got this when building a project via Visual Studio Online (VSTS) Build using Visual Studio Build Steps.

The solution was:

Delete the existing source folder

Explicitly set 'Any CPU' in the platform for all Visual Studio Builds including dependencies (see screenshot below).

Re-run the build

https://i.stack.imgur.com/8qqWz.png

---

The Chilkat .NET 4.5 assembly requires the VC++ 2012 or 2013 runtime to be installed on any computer where your application runs. Most computers will already have it installed. Your development computer will have it because Visual Studio has been installed. However, if deploying to a computer where the required VC++ runtime is not available, the above error will occur:

Install all of the bellow packages

Visual C++ Redistributable Packages for Visual Studio 2013 - vcredist_x64

Visual C++ Redistributable Packages for Visual Studio 2013 - vcredist_x86

Visual C++ Redistributable Packages for Visual Studio 2012 - vcredist_x64

Visual C++ Redistributable Packages for Visual Studio 2012 - vcredist_x86

---

For the newer version of visual studio (v16.10 for this answer), it can be fixed by manually changing the solution platform. For me it worked after changing from "Any CPU" to "x86".

Click on solutions platform dropdown, the one in which any CPU is appearing in image below. Go to configuration manager. Click on new and add platform x86 or x64 (32 or 64 bits) based on what is working for you. Restart the project.

---

You might also see this issue if you're trying to package a 64bit project with an MSI installer in VS. ("The reason is because the native shim packaged with the .msi file is a 32-bit executable.")

See here for more details: http://blogs.msdn.com/b/heaths/archive/2006/02/01/64-bit-managed-custom-actions-with-visual-studio.aspx

---

I encountered the same issue. It popped up out of the blue and that seemed strange to me.

In the Exception snapshot, for the FusionLog, I saw the following within its message:

... C:\Windows\Microsoft.NET\Framework64 ...

More about the fusion log: http://msdn.microsoft.com/en-us/library/e74a18c4(v=vs.110).aspx

All the projects had a Target CPU of AnyCPU. I changed the application project (the project that references all the other projects) to a Target CPU of x86. It now works.

Not sure how the Target CPU mix up occurred for no apparent reason, but it did.

---

I also face this problem in a project, after a few minutes i found the solution, this problem is due to CPU configuration, If you are using Visual Studio 2010 or VS 2013, just goto project 's properties and then select Compile from side bar and there will be 5 drop-down, 5th Drop-down will be Target CPU:, you should set it to x86 or x64 according to your requirements instead of Any CPU.

My problem was solved after changing it to x86.

---

This also can happen just by having multiple supported frameworks defined in the app.config file and, forcing the app to run in a different .NET framework other than the one mentioned first in the app.config file.

And also this fires when you have both of the mentioned frameworks available in your system.

As a workaround, bring up the target framework you are going to use for the debugging up in the app.config

ex: if you trying to run in .NET 4, config file should have something similar to this,

<supportedRuntime version="v4.0"/>
<supportedRuntime version="v2.0.50727"/>

---

In my project for C#, project property->[Build]->Platform target: Any CPU, and uncheck the Prefer 32-bit to let compiler to choose automatically.

---

I also had this problem running unit tests by using ReSharper on Visual Studio 2017 and fixed it with following config:

https://i.stack.imgur.com/ebsH5.gif

Also you can change the ReSharper's run test setting: https://resharper-support.jetbrains.com/hc/en-us/articles/207242715-How-to-run-MSTest-tests-using-x64-configuration

---

Shoot! I knew about this problem. I thought I was doing everything right until I accidentally saw 'x86' in the VS output window and that's when I got hold of the cause. Wasted a few mins on it today.

The configuration under 'Publish' window was set to 'x86'; whereas, everywhere else, it was 'x64'.

Please make sure it's in-sync across configuration manager, publish settings, solution configurations, and IIS settings (if that's your web server).

Also, please keep in mind - VS is a 32-bit app and IIS is 64 bit. 32-bit apps are disabled by default in IIS.

https://i.stack.imgur.com/0vXGy.png

---

It can be a little funny, but I had the same problem with normal working code. I added StreamWriter and StreamReader and it gave that error. The solution was I took that code into comment brackets then did debug and it started to work again

---

If you use LibreOffice from your program via cli .net integration like me, I got the same error. I use the older version of LibreOffice on the production environment on my PC I installed a newer version that was in conflict. Just uninstall LibreOffice. I found the solution here .NET CLI: Could not load file or assembly 'cli_cppuhelper'

---

In my case a dependency was missing in the dll that threw this exception. I checked with Dependency Walker, added the missing dll and the problem was resolved.

More specifically, I somehow corrupted my opencv_core340.dll by accidentally adding SVN keywords to it, and thus my dll could no longer use it. However I don't believe that the solution to this problem depends on whether the dll is corrupted or missing. I'm just adding this for the sake of giving complete information.

---

I have detected something different from the other answers. Reaching this exception in my project was the result of a corrupt compilation. Without making any changes, just forcing rebuild, it was fixed.

---

I had the same issue. Project B in my case was a .Net Core Class Library which has a Nuget "Microsoft.Management.Infrastructure" installed. The error was that i called my project B "MI". I changed the project name to something else and suddenly everything worked again.

---

Interesting as it goes, this can also happen if the folder path is long, which can cause build issues, oddly enough with this cryptic error message.

Just moving the folder up the path, solved the problem!

---

Are you trying to run your .exe file from the cmd? This was my mistake. Just run the .exe file by double clicking it. If it's a .NET Core SCD for Windows 8.1/Windows Server 2012 R2 x64.

---

In my case the error was System.BadImageFormatException: Could not load file or assembly 'vjslib, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a' or one of its dependencies.

It was solved by installing vjredist 64 from here.

---

My machine showed me a BIOS update and I wondered if that has something to do with the sudden popping-up of this error. And after I did the update, the error was resolved and the solution built fine.

---