I believe that the Maintenance Clean-up Task can only clean up backup files created directly by the Back Up Database Task. As far as I remember, LiteSpeed backups can only be invoked by calling an extended stored procedure, and so have to be set up using the Execute T-SQL Statement Task.

Unless you are able to use native SQL Server backup rather than LiteSpeed (allowing you to use the Back Up Database Task), it looks like you will have to write a script manually to find and delete old files. Be very careful with this, as it is all too easy for a bug in the script to delete files it should not.

Paul