Carbon Copy Cloner -- Destination Drive Full?

[Moosbrugger]

I'm using CCC to backup my 750 gb iTunes library onto a 1 tb external drive.  It's now telling me that the external drive is full.  I turned off and deleted the safety net, and set CCC to run a deletion pass first.  But I'm still getting the error message.  So, the target drive should have the same 750 gb as my source drive -- but it's still telling me that the target drive is full.  Any suggestions?  Thanks.