What exactly is the error message you are seeing?  Have you tried using Gearbox instead?  Please go the following link to download/install the Gearbox 3.70 software for your Leopard Operating System, which also includes the Line 6 monkey intelligent updater and the latest drivers for your Line 6 product.

  http://line6.com/software/

  Copy/paste the following links (beginning with http) into your internet browser for additional Line 6 software information:

  Line 6 Monkey Installation and F.A.Q.

  http://line6.com/community/docs/DOC-3898

  Mac: USB Device Driver Installation

  http://line6.com/community/docs/DOC-1773

  Use the information in this link to optimize your computer to work with Line 6 Gear:

  Computer System Audio Optimization

  http://line6.com/community/docs/DOC-4201

  See your manual for more application information:

  Gearbox Program manual

  http://line6.com/community/docs/DOC-4839

  See the following information for setting up your Line 6 device as the soundcard on your computer:

  Setting up Line 6 device as External Sound Card on a Mac Computer: Video Tutorial

  http://line6.com/community/docs/DOC-1487

  Assigning your Line 6 Device as a Sound Card on your Mac Computer

  http://line6.com/community/docs/DOC-1454

  If you are still having problems you should try a different computer to see if this changes the situation.