Export request stuck at failed - user isn't a mailbox user

Hi,

on our exchange 2010 SP1 (don't ask why it's not updated) I got a user which is no longer with us in the company. User is disabled for a long time but still in AD. After I export a mailbox for another user and run the get-MailboxExportRequest -status completed | Remove-MailboxExportRequest I get a "leftover" user and status failed.

Then I run: get-MailboxExportRequest -status failed | Resume-MailboxExportRequest

I get an error message: company/OU/user isn't a mailbox user or mail-enabled user.

I inherited this situation from a college which administered our Exchange environment before so I don't know what has been done.

Thanks,