You can alos use Enterprise Manager to set the default database:

1.  Expand the SQL Server Group in the left pannel.

2.  Expand the Server

3.  Expand Security

4.  Select Logins (also in the...

Try rewritting your query a little:

Here is my update statement:

UPDATE    o

SET              SerialNumber =

                          (SELECT     t.SerialNumber

                            FROM       temp1 t

                            WHERE     o.Un_ID = t.un_id)

FROM Objects o