Runtime newer than Currently Loaded

Failure adding Assembly to the cache: The assembly is built by a runtime newer than the currently loaded runtime and cannot be loaded.

So, today I was building a reporting application with DevExpress Xtrabase Report Suite. (So far great reporting tool). Building it on my machine with VS 2010 and .net Framework 4.0. Everything worked well on my machine. So now comes time to deploy to Development box. Development box is running IIS 6 with .Net Framework 2.0. When I ran the GacUtil tool I received the above error. After some digging I found that I either had to do one of two things. Install .Net Framework 4.0 or recompile my application in .Net Framework 2.0 - 3.5. So since I wasn't using anything specific to 4.0 and I didn't want to spend all day installing software, i opted to just change the properties of my application to build in 3.5. Copied to the dev server and reran the GacUtil and Bajinga... everything worked...