Exception not handled, how to fix?

Question

C++ / C#

every time IIS Express starts I get this problem

Answer 1

If the error only occurs when using IIS Express, then just don't use it like normal IIS - there's really no reason to use them right now.
In general, everything is written in the error - if this folder really exists, then IIS simply cannot access it (another reason not to use it)
Look at how this path is set in the config - you should probably use a relative path instead of an absolute one, and copy the plugins to the application folder.
PS: are you trying to launch nopcommerce by any chance?