What version of Desktop Manager are you using? I upgraded to 4.5 and got a similar error, tried 4.6 and found the same. I moved back to 4.3 and it magically worked again.
Did you recently install any new application? I installed the application that gives you pop-up of your emails. After that install I couldn't back up my . I uninstalled the application. Backed up my and reinstalled. Try that see if that helps.
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