Restoration of Online Backup Failed

I had to do some inventory adjustments and I made an online backup as a precaution before I did it.  This was after hours so no other uses making changes to the file.

Processed my adjustments, wasn't happy with the result.  Went to restore the online backup.

It warned me it could take a while.  So I sat around for an hour cleaning out my email inbox while the restoration processed.  

Got to about 98% and then suddenly a screen message pops up that backup restoration has failed and no changes have been made to the file.  Doesn't tell me why it failed.  

Excuse me?  What am i supposed to do now?

I didn't have another hour to sit around and wait for the backup restoration to fail again.  The adjustments needed to be made before the staff started work the next day, it was already after 7pm.  Fortunately I was able to delete the adjustments and that seemed to have no ongoing effect on average price, and I achieved what I needed to via general journal.  

Still, what am I supposed to do next time I need to restore a backup and it fails?