This problem occurs because SQL Server 2005 cannot obtain the information about the context when you try to impersonate a database user to run a statement or a module.
SQL Server cannot obtain the information about the context that you are trying to impersonate under the conditions that are listed in the "Symptoms" section. If you impersonate a SQL Server authorization login, SQL Server cannot find a login that matches the security identifier (SID) of the impersonated user. If you impersonate a domain user, the domain controller cannot find the information about the specific user who matches the SID of the impersonated user.