Error : Type SP.PermissionKind has already been registered.

The error occured while using the javascript client object model in my applciation page. After searching alot on google i finally found out that any refrences of the js files made twice would cause an exception like this.

Whats was i doing? - I was adding a refrence to SP.js file and was also using the ExecuteOrDelayUntilScriptLoaded(something, "sp.js"); in my applictaion page. This caused the "not very explanatory" error. Removing the scriptlink fixed the issue.