Best of luck mate, this 'bug' with 8.1 OS has been around for as long as 8.1 and still no fix from MSFT. Everyone will tell you to delete old backup, turn of text backup, change lock screen picture, remove apps (?) etc, etc,. Like many many others I have tried just about every combination of 'fixes' and never got this lame excuse for a backup to work. When my partner was recently prompted by her L620 to backup she duly tried - only to get the same "There was a problem... " error message. Anyway note that even if you do get some sort of backup to run it will not be a proper device backup, just 'links' to re-install apps etc. There is no Windows Phone device backup that I know of and MSFT seem disinterested in providing one that works.