As MDM consultant, we archive and unarchive repositories during different phases and in different contexts.
I was trying to unarchive the production copy repository in Dev landscape and ended facing consistently issue of 'Unable to modify Database' as shown in below screen shot.I was not sure of what was happening. I tried to stop/start MDS, unmount and mount repository in console etc...during which I wasted productive hours.
Finally, I got to know from my colleague that the issue is due to space issue. If the server does not have sufficient space for unarchive, then we face this issue. I wrote this blog with intention of may be this will be of help for others as quick reference instead of wasting time to once again reinvent the wheel.