Can you run the CHECKDB using WITH TABLOCK?
Can you also try creating a database snapshot of your database to see if that succeeds? (nothing to do with CHECKDB)
I suspect there's something amiss with it and when the snapshot creation starts, it's trying to roll back a transaction in the snapshot and failing.
Paul Randal
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Blog:www.SQLskills.com/blogs/paul Twitter: @PaulRandal
SQL MVP, Microsoft RD, Contributing Editor of TechNet Magazine
Author of DBCC CHECKDB/repair (and other Storage Engine) code of SQL Server 2005