In AccuZIP6, pull down File to Print Presort.
In the Print Presort window, make sure your presort for this job is open.
Click on the button (with the red X on the folder) next to the Job ID. This will create two files in your presort folder: A Cancel file and a Delete file.

In PostalOne, hit the Add Jobs link and, instead of selecting the maildat.hdr file like you typically do, select the Cancel file. Choose the Validate and Upload option. Once that file uploads successfully, perform another Add Job, then add the Delete file from your presort folder.
After that uploads successfully, perform a third upload to PostalOne. This time, upload the maildat.hdr file. The upload should be successful and the job should now show up successfully on the dashboard.