RadScriptManager error in DotNetNuke module

[mohsinjk jk]

Hi 

I am working with RadSriptManager in web usercontrol. when i use it on my page it give me following error

"A critical error has occurred.
Object reference not set to an instance of an object."

I read some thread about this problem but not found any solution please guide me how i can use this control in DotNetNuke modules. 

Thanks
Mohsin Javed Khan