Validation (): Element 'xxx' is not supported

Hi,
I am getting this error in aspx page and I found a solution for this. I'm getting this error for each tag I used in the page.

Computer -> OS (C:) -> Users -> {username} -> AppData -> Roaming -> Microsoft -> VisualStudio -> 9.0 folder. In this we have to delete "ReflectedSchemes" folder. But I don't have access to this path.

Is there any solution for this?