USB Problems Vista Host OS Ubuntu Guest OS

[FearlessLeader]

I am trying get 2 USB network adapters to work at the same time on Ubuntu as the guest OS using Virtualbox. The PC is a slimline HP so I didn't have slots for network adapters. I'm inserting an image to show the error that occurs when I click the second USB network adapter to activate.

http://www.collegestation.com/usberror.gif

Thanks for any suggestions.