I've received that same error message when performing a simple delete-statement ("delete from rpt_reports where createddate<'2013-04-01'") - the message I get is:

Msg 4060, Level 11, State 1, Line 65536

Cannot open database "xxx" requested by the login. The login failed.

Msg 18456, Level 14, State 1, Line 65536

Login failed for user 'xxx'.

I tried to execute the command form server management studio, and I was logged with integrated security. I had no problems executing other commands like "select count(*) from rpt_reports") in the very same window?!?

...any ideas?