Back up problem: Error 503

I assume you are trying to RESTORE a backup? If so, is this backup on a location such as CD media? If so, copy the .BAK file to your hard drive then attempt to restore again.

Logbook Pro does not support backup/restore operations to/from CD (optical) media.

As stated above, Logbook Pro does not support CD media, please create the backups to your local hard drive, then you can close Logbook Pro and use any other program you wish to write the created .BAK file to your desired media.