-24990: ERR_ NOBACKUPSESSION - no backup session available 

Explanation:

The DBM command is only permitted if the Save or Restore is active.

User Action:

First start the backup session you require using the backup_start or recover_start DBM commands, then execute further commands depending on how the Save/Restore runs.

Check whether the save/restore process started properly.

Please note that reading a database backup will override the current state of your database instance.

If the error occurs in Database Manager GUI and there is no way in which you can correct it, please contact Support.