I would try to run it for some other database to see if doesn't work in general or doesn't work for this particular DB only.

>Nope - try that and it "completes succesfully" but not guest user is in the database (EM or sysusers)
>
>???
>
>>

USE myDB
>>execute sp_grantdbaccess guest

works for me from QA (SQL Server 2000, sa login).
>>