Norski,
I haven't ran into an issue like this, I am hoping you can provide a little more information while I research possible causes:
When you say "forget" do the devices not show up in Windows device manager, or just in Measurement and Automation Explorer?
What brand/model are the PCs with the issue? Are they the same as your other systems that work? Also, are they all on SP 2?
Also, which version of the CAN driver do you have?
Normally I would like to have you test individual cards to see if a specific one was causing the issue, but that may not be an option with the long repeat time. One thing to confirm though would be that the individual cards work as expected before they don't show up.
As far your concern with the IRQ numbers, I'm not sure how this could be in play. My understanding of IRQ is that it only has 16 lines (lines 0-15). There are also 8 lines (0-7) of DMA - this could account for the 22 lines if things were read incorrectly. Do the older systems not have DMA lines?
Thanks,
Andrew