Files don't save

We are using a Drobo S as our main file share installed on the domain controller. We’re having a problem that when users open a document, make changes, then click save, the updated file isn’t being saved. I have verified that it is not user error. This problem started right after I installed the Drobo S, which is why I suspect the Drobo. Has anyone else seen this issue?
Our environment is:
Windows SBS 2008
Drobo S on eSATA (disk drive spindown set to ‘never’)
31 domain users


Where is said file being saved? On the Drobo S, or on different storage?