Not SQL Server Encryption, 3rd party encryption on the O/S (e.g. TrueCrypt etc.). Or a new install/upgrade of a defrag tool like DiskKeeper. This is likely something at the OS/Storage level that's preventing a snapshot from being created (this is NTFS functionality).

Article from Paul Randal here:

http://www.sqlskills.com/blogs/paul/search-engine-qa-14-beware-3rd-party-file-system-drivers-with-dbcc-checkdb/