I\'ve got vs2010 and vs2012 installed side by side. If I open up our MVC site in vs2010 and run it using the development web server it works fine, if I do the same thing in vs2
** Config.XML is the first place to begin research ** on new Windows Visual Studio 2012 install. The values should be manually reviewed on each new client/server application
When truly inappropriate server errors make no sense at all, think about your test computer's config XML files that set queue or pool sizes explicitly in the project root, as described in the above MS link. It's highly odd that a server would respond "Too Busy" when it's just you on the machine.
Always good to be able to reuse as many recyclable objects as possible, in particular, database connections.
As far as running both VS 2010 and 2012 on the same development machine it should be ok. Just check there your references are pointing for application dlls.