The xbm command line configurator that you are using is actually still under development.
Many of the documented commands in the help output do not actually do anything, nor do they return any errors.
Unfortunately I think "delete" is perhaps one of them.
In addition, right now you must use the xbm-flush command to flush your schedule to the crontab - it does not happen automatically.
This will change once the xbm command line configurator is complete.
I'm actually hoping to finish this up over the next few weeks - so my apologies for the half complete tool you are experiencing right now.
I'm glad to see that you somehow managed to get things going a little.
I hope you'll stay tuned to my blog and/or the Google code project and try it out again once I have actually finished the development!
Right now if you want to DELETE the scheduled backup you created, I believe that you will need to go into the database and DELETE the row from the scheduled_backups table corresponding to the scheduled backup you created.
Note: This is really a hack and will leave some orphaned rows behind -- as I said, this will be all handled by the xbm command line tool once it is finished.
Best Regards,
Lachlan