Please help us to fix it... It displays an error as follows. "[XNRR7V010].DBO.[OSSYS_USER_T13] with key 0 was not found" 

I guess that you are using the GetUser action of User Entitie and you are passing 0 as ID.
If you pass an Id that doesn't exist in that kind of action it will give an error.

Just to complement the above info check this information.
ok. Thank you. It helps.