When you open a project in VS 2010 it asks you if you want to upgrade the project to target .Net 4.0 and has a checkbox to do this to all applications. The first time every project opens it gives me this prompt and I always click no.
This time I accidentally clicked yes and it had the checkbox checked to do this to all project. I reset my settings and looked through the options, but can't find the setting to get it to stop trying to update my projects.