Visual Studio Addin failed to load

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If you are developping a VS addin or even if you are just a VS Addin user you certainly met this popup message in the past at VS startup time:

I can attest that this message box popups because of environment issue including:

  • Missing file(s)
  • Mismatch 32bits / 64bits mode
  • Security issue: maybe one of the hardest to pinpoint: blocked DLL. A DLL might be blocked when unzipped on your hard-drive for security issue. Brad Abrams reported as well this problem here. You then need to unblock the Dll file addin entry point.

The main problem is that VS Addin developers don’t even get a chance to prevent problems because typically, the popup message is shown before any IL instruction of the Addin get executed!

So at the very least, it is essential that the VS Addin loading failed popup message displays error message that are actually useful. Because it is an environment issue, the VS user could solve it easily by himself without all the friction of reporting the problem and waiting for a solution. For example I obtained the popup image above by deleting NDepend.Addin.dll, why don’t I get a clear message like: missing Dll file xxx ?

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  • http://huagati.blogspot.com KristoferA

    One more common reason to add to the list: If the user uses roaming profiles and/or has his VS add-in directory on a network drive / UNC path… …the assemblies will not be trusted, and VS will fail to load the add-in. Easiest workaround for that one is to move the add-in files to a local directory and add that directory to the VS add-in load paths…