I have several Quatech dual port PCIe serial cards that fit in PCIe X1 or higher slots. My understanding of PCIe XI cards is that they will work in X1, X4, X8, X8/16 and X16 slots. Indeed, when installed in any PCIe slot on the motherboard, Windows detects the card, and doesn't report any issues or conflicts. However, when installed in certain PCIe slots I cannot establish a serial connection over the COM port. Put another way, the same card will work in an X4, and X8/X16 slot but not in an X1 or X8 slot (even though Windows detects the card with no issues in any of the slots - IRQ and I/O range report no conflicts).

I don't have much of an understanding of PCIe, but I find it strange that Windows detects the card without any issues, but I can't establish any serial communications when the serial card is installed in some PCIe slots.

Can anyone enlighten me?

I'm running Windows 7 64-bit