DBO.[OSSYS_USER_T9] with key 0 was not found

DBO.[OSSYS_USER_T9] with key 0 was not found

  
I can´t find the answer for this error, can anyone please help me? I was trying to add an newitem by the popup editor. 
Ivan -

You are using "GetUser" but using a null User Id.

J.Ja
J. Ja thanks a lot, i finally find the error with your help.