No compiled code to run Error BC30560 - Invoke code activity

I HAVE USED VB.NET code INSIDE AN invoke code activity but getting this error . Dont know why ?
error BC30560: ‘ExtensionAttribute’ is ambiguous in the namespace ‘System.Runtime.CompilerServices’. At line -20
error BC30560: ‘ExtensionAttribute’ is ambiguous in the namespace ‘System.Runtime.CompilerServices’. At line -5
error BC30560: ‘ExtensionAttribute’ is ambiguous in the namespace ‘System.Runtime.CompilerServices’. At line 10

Hi!

Import this namespaces from imports panel

Regards,
NaNi