Just leaving a note for anyone else who is looking for an answer and ends up here like I did.
(I assume unsichtbare has long ago sorted his particular issue.)
I just spent an afternoon on this and found a leftover snapshot that had blown out to half a GB which made the commit time very long, which caused auth issues when the clock jumped forward 15 minutes or so at the end of each commit. (Flexlm hates that FYI)
For me
Takeaway /1
>> In vSphere, Inventory, Datastores and Datastore clusters;
>> select the "Datastore" then check the last tab called "storage views" .. scroll down along the "snapshot storage" column. Anything that's not 0 or 45 kb indicates a snapshot.
Takeaway /2
Check this manually or scripted, however you normally work on some sort of regular basis. ("veeam one" if you have veeam)
Rule-of-thumb is all snapshots should be cleared before backups begin.
While it's vmware function (or just plain IO but the OP and my kit should both be fine), the veeam guys have it covered in this -- Community Forums • View topic - Snapshot removal issues of a large VM --post. it's 13 pages as of Aug2013, skim backwards I guess.