I don't think that that is the issue because

-I am running the query through SSMS

-I am logged into SSMS (both the query and the object explorer GUI) using sql credentials...

Thanks guys.

Nicholas - good call. I changed the login to be a domain user instead Local System, restarted the MSSQL Service and was able to add the user.

Brandie -...

Hi Brandie,

Thanks for the response! Unfortunately running both without dynamic sql (and therefore no variable) or running the entire statement as one variable in the exec command failed...