The login needs to be a member of the securityadmin server role.

Try sys.database_mirroring. This table contains a column called mirroring_witness_name.

I can address the login but not the jobs. Look for this article. 'Login failures connecting to new principal after failover using Database Mirroring'. It was published...

Grant execute on sp_sdidebug to your user.  One of the service packs changed permissions on this stored procedure.

Have you tried scptxfr.exe?  Take a look at the following link.

http://www.norbtechnologies.com/pdf/Technical%20Article%20-%20How%20to%20Schedule%20a%20SQL%20Server%20Database%20Creation%20Script.pdf