After upgrading to LiteSpeed for SQL Server 5.1.1, backup jobs in maintenance plans with verify backup and encryption options started failing. Event viewer and LiteSpeed logs showed the following error message:
Msg 61101, Level 18, State 1, Line 0: The backup file is encrypted, and you have not supplied the correct decryption key for this file.
Note: The decryption key is the same as the one used to create the backup file.
Uncheck either the "Verify backup when finished" or "Encrypt backups". Having both options enabled will cause the error.
Waiting for fix in a future release of LiteSpeed for SQL Server.