What does the SQL Server error message "sort: bob write not complete after xx seconds." mean?

A. Bob is the Big Output Buffer. It is used for writing out intermediate tables created during a sort. Because it is doing heavy sequential writes it can stress the disk subsystem.

As long as SQL Server carries on, and no other errors are being reported, then there is nothing to worry about. They are merely showing that the disk subsystem is unable to keep up with the level of i/o that SQL Server is asking it to do. SQL just waits and retries these requests.

To up the amount of time that SQL waits before issuing this message and retrying amend the "resource timeout" parameter via sp_configure.

You MAY need to decrease your max async io or max lazywrite io if these errors are continuous. Or invest in a faster disk subsystem. Or spread your devices across more of your existing spindles.

Also make sure that non-SQL processes are not causing disk contention.