Visual Studio :: From VS2008 To VS 2010 Created A New Class?

I've just upgrade my web application from vs2008 to vs2010, I create a new web app from vs2010, then copy across all the existing files from vs2008, then I add a new class file to App_Code folder, the intellisense is not showing up for everything and class etc is also not color in the right color. However, when I open the existing class I created earlier from vs2008, intellisense just working fine and all classes are in different color as well, if I make a copy of existing class, the copied class does not support the intellisense as well. However, if I shut my VS, and reopen it, they all appear to be support with intellisense for existing class, but once I created a new class, intellisense is not support.