The DBM server statement is only permitted if the Save or Restore is active.
First of all, start the backup session you require using the DBM server statements backup_save or backup_restore and execute further statements depending on how the Save/Restore runs.
Check whether the Save/Restore started properly.
Note that importing a database backup using Restore will override the current status of your database.
If the error occurs in the Database Manager GUI and there is no way in which you can correct it, contact your local support organization.