Sep 27, 2009 09:33 PM|cnuauk|LINK
I can tell you exactly what was wrong and how to put it right, also this would be of help to anyone with the same problem browsing this thread.
The problem occured because your Target Framework setting was probably
.Net Framework 2.0 while system.web.extension 18.104.22.168 requires .Net Framework 3.5.
To reproduce the problem on VS 2008 SP1, add a reference to system.web.extension while the Target Framework (In Properties/Application) is set to .Net Framework 3.5, your project should compile ok. Now change the Target Framework to .Net Framework 2.0 then
try to complie the application, you will get compile errors, notice also the exclamation icon next to the system.web.extension in your references folder (if its a c# project) which indicatesa missing reference
Do mark this as the answer to a compiler version problem as you see fit