Upgrade ASP MVC project from VS2008 to 2010 - is it possible not to upgrade to .net4 at the same time

I have a Vs2008 project using version2 of the ASP MVC framework. I tried to upgrade to VS2010. I fetched a new copy from svn and opened it. I got the expected conversion dialog, clicked next and then finish. A while later comes up a question do I want to also upgrade to the version 4 of .net framework.

I've done this same process twice wioth开发者_JAVA百科 the same project. THe first time I clicked no and the second time I clicked yes. But, if i run a diff across the directories created, there's essentially no difference (some generated dlls differ and there's a path difference in the vbproj file but that's it). If, however, i diff the new and old project I get a whole load of differences. That's of course expected, but some of them seem to indicate that it's done the upgrade to .net4 anyway! For example, the vbproj file now referneces 4 instead of 3.5 as it's tools version and all the reference.vb files generated from the .wsdl files for my web references now have "Runtime Version:4.0.30319.1" instead of "Version:2.0.50727.4927" and Resources.Designer has a similar.

So, my question, should there be a difference between the version where I said "yes, upgrade the -net framework to version 4 for this project" and the version where I said no or does ASP run with the old version anyway? I really don't want to find that my new version doesn't work when deployed to production servers which may not have .net 4 installed!

You can always change it back to 3.5 in the project settings, so long as you don't upgrade the MVC version to MVC3. Some of those settings may say 4.0 because they depend on the VS2010 designer, which is based on 4.0, and thus needs to reference 4.0 versions at design-time.