Silver light Debuging Error

Question

 i am using silverlight 4 with vs 2010(C#)

When I Press F5(debug)First it gives me this Error

1)Unable to start debugging. The application uses a version of silverlight that isn't supported by this debugger."

and when i pres "Ok" button 

it gives me 1 more error

2) Unable to attach to application iexplorer.exe(PID:2596) a debug component not Installed.Do you want to Continue anyway ?

how to get rid of it