Sadly this is what happens when the mailbox corrupts.
You could try getting the jobs via the software (Fiery Remote Scan) instead of the webpage, but it is probably a lost cause.
Assuming nothing critical is on there, just clear out the mailbox of all scans (CWS5 > Server > Clear Server > Scan).
Reboot and try another scan.
If it doesn't begin to work on the new jobs you would need to create another mailbox to use or reload the Fiery.