Roel,

It's absolutely not the USB port of the TYROS that locks up.

I need to reboot the PC to recover the connection while the TYROS is kept on. So it looks like that a noise/spike on the main connection of the TYROS causes the an unwanted signal over TYROS USB connection that causes the PC USB port circuitry to locks up.

I tried other equipment on the PC USB port - no problem. I tried the same with a Laptop with W2K, same problem. During reboot of W2K hangs in a "blue screen" with error message that indicates that IRQLines are lost/wrong.

Regards Jaap Veneman