wwww_wu：http://geekswithblogs.net/cyoung/archive/2007/12/01/117279.aspx|@||@|There is no switch to flip your Visual Studio 2005 to use the 3.x framework instead of 2.0.|@||@|You have to right click on your web (or other) project and get into your "project references." That's the long list of libraries that might including things like:|@|System.Web|@|System.Data|@|System.Xml|@|etc.|@||@|If you want to use the 3.5 framework you either have to START with a project that has all of these already pointed to the 3.5 libraries (using a template), or you have to take the time to manually add each and every individual reference that you need.|@||@|Remember, each of those entries in that long list is a library and the .Net Framework itself is just a collection of LOTS of these things. Now, as stated above, some of the libraries didn't change when the .Net Framework 3.5 was released, so you might be confused by the version number and think, "hey, my System.Web library isn't using the 3.5 Framework." Don't worry about that, you didn't miss anything, you are just seeing where the line has been blurred a bit because the library didn't change.|@||@|If you click Add Reference and go to the .Net tab, you will also see lots of libraries that have the 188.8.131.52 version. This is the new stuff that you didn't have before you installed the 3.5 framework. If one of these libraries has a feature you need, go ahead and add it to your project, but again, don't get too hung up on those 2.0.xxx numbers that still seem to be hanging around in your project references.|@||@|So, I hope this was a help. I know the answer that was "desired" was flip this switch and POOF you are running the 3.5 framework in VS 2005, but I can't really offer that for you.|@||@|Fortunately, later versions of Visual Studio get much better at providing the user with a clear picture of which framework to "target," but I wont get into that because it's a much longer post.