Why am I getting "Unable to find manifest signing certificate in the certificate store" in my Excel Addin?

You need to re-add that certificate to your machine or chose another certificate.

To choose another certificate or to recreate one, head over to the Project's properties page, click on Signing tab and either

Click on Select from store

Click on Select from file

Click on Create test certificate

Once either of these is done, you should be able to build it again.

I found this solution which solved the problem for me: Removing all entries in your *.csproj that fall into:

<manifestcertificatethumbprint>...</manifestcertificatethumbprint>
<manifestkeyfile>...</manifestkeyfile>
<generatemanifests>...</generatemanifests>
<signmanifests>...</signmanifests>

A quick solution to get me going was to uncheck the "Sign the ClickOnce manifests" in: Project -> (project name)Properties -> Signing Tab

When the project was originally created, the click-once signing certificate was added on the signing tab of the project's properties. This signs the click-once manifest when you build it. Between then and now, that certificate is no longer available. Either this wasn't the machine you originally built it on or it got cleaned up somehow. You need to re-add that certificate to your machine or chose another certificate.

Adding new certificate resolved this issue for me. Properties page -> signing -> Click on Create test certificate

Make sure you commit .pfx files to repository.

I just found *.pfx in my default .gitignore. Comment it (by #) and commit changes. Then pull repository and rebuild.

Delete these entries mentioned in this post: http://manfredlange.blogspot.ca/2008/03/visual-studio-unable-to-find-manifest.html. Also remove the .snk or .pfx files from the project root.

Don't forget to push these changes to GitHub, for Jenkins only pulls source from GitHub.

The issue of erroneous leftover entries in the .csproj file still occurs with VS2015update3 and can also occur if you try to change the signing certificate for a different one (even if that is one generated using the 'new' option in the certificate selection dropdown). The advice in the accepted answer (mark as not signed, save, unload project, edit .csproj, remove the properties relating to the old certificates/thumbprints/keys & reload project, set certificate) is reliable.

I create a new key, I had to search the csproj for the old one and refactor it.