Dang, happened again one month later after weeks of success. Unfortunately, from what I learned last time I spent time investigating; I really have no control to get any files for this to a test environment nor to execute dbcc on production outside my weekend window.

2005 SP4, Standard - with all primary databases on the same RAID 10, 8 disk volume. A DBCC even from snapshot would slow the IO down too far during weekday operations, even in maintenance periods, to allow for good normal operation on data input and output. Only time I really can run the DBCC stuff due to IO stress is on the weekend, when it is scheduled to run.

I checked for auto growth thinking maybe the files where in a growth, but saw nothing for that particular database.

Related found content:

http://msdn.microsoft.com/en-us/library/aa337285.aspx

http://connect.microsoft.com/SQLServer/feedback/details/241265/attempted-to-unlock-a-resource-it-does-not-own