The DBM command is only permitted if the save or restore is active.
First of all, start the backup session you require using the DBM commands backup_start or recover_start and execute further statements depending on how the save/restore runs.
Check whether the save/restore started properly.
Note that importing a database backup will override the current status of your database instance.
If the error occurs in the Database Manager GUI and there is no way in which you can correct it, contact Support.