sounds like you might be both suffering from a low powered USB. Maybe your using a unpowered HUB or front mounted USBs. Ive noticed you dont always get enough power to these and because of this your better off running off the main USBs mounted straigh onto the board.
If i plug in my PSP to USB hub keyboard and also have my HP 5550 in at the same time my PSP doesnt charge and will run on batteries. You could always test the volts coming from the USBs your using. Jus be careful not to short anything out, PC or PSP.