.NET - does not exist in the current context

I have a few apps built in ASP.NET 3.5, VS 2008. After having to re-install VS 2008, when I go to amend any page in any system, all the controls dont seems to be recognised and Im faced with "[control name] does not exist in the current context" This is for all my apps. Also getting "failed to create app domain" in all开发者_开发问答 apps as well. Any idea's what Ive done?

Thanks

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sorted it in the command prompt with caspol -reset