We have a QNAP 24TB NAS box attached to a couple of our file servers (Server 2008R2) via iSCSI.

In general they work ok, but a few times a week we get users reporting problems when saving files (especially MS Office files) saying they are getting a 'File already in use' message (the file isn't actually in use by any other user).

I have checked all of the usual stuff like permissions, file ownership etc....and nothing obvious appears to be wrong.

I have read somewhere that this kind of error is something to do with NAS servers, but cannot find the article.

Does anyone know what might be causing this issue?