I can't get two Gravis Gamepad Pro USB controllers to work together.

[Karnalis]

I recently bought a second Gravis Gamepad Pro USB to go with my first, so I could use them for 2-player games. When I plug it into my computer, however, it causes problems with my first gamepad. The second gamepad works perfectly, while the first gamepad now constantly registers button-presses as though I were holding down the buttons, even after I release them. The Gravis site reported a similar problem for different types of gamepads, and mentioned the possibility of a DirectX data stream issue, though I'm not sure why that should be the case (I have DirectX 9.0c on a very fast PC, and dxdiag reports everything working correctly). Is there anything I can do to get my two gamepads to behave and play nice together, without messing each other up like this? I'd love for both of them to be usable simultaneously. Thanks in advance for any advice you may have to offer!