Make sure that's 3.5, SP1 per new MS Lifecycle policies.
http://www.craigberntson.com/blog/?p=854>
>So far I'm still doing ASP apps using .NET 3.5. I haven't done a 4.0 site yet although I am using VS2010 (and I like it!).
Craig Berntson
MCSD, Microsoft .Net MVP, Grape City Community Influencer