I've found the root cause......Just update OS/2 AMD PCNet NIC driver to 4.08, and All's OK.
The older driver in all probability (from the message, if it was properly used) could have had identifying information specified (method indicated below).
While I know you've got this issue solved (and others who may use that card can follow your method to resolve it), this issue also applies to a variety of other NICs.
For anyone else who runs into such:
The required info could be added via MPTS (or directly into the config.sys file - which requires knowledge of how the parameters are used). Especially if an IRQ ends up being shared, such info is needed with certain drivers. That info is usually an assigned address range, or a slot ID (in some format determined by the driver, ie: by number or by the way the chipset identifies it).
It's really as simple as using MPTS to select each card, modify it's properties, look for the slot identifier field, and enter in the correct information. Most cards/drivers that require such will inform you (on the MPTS settings page, or via the help pop-up) what format is needed.
Now, there are a few cards that simply wont work under OS/2 (and possibly other operating systems) when 2 or more are installed... in such cases, you wont find a slot identifier field in the MPTS card properties.
The same of course applies to cards that are "autodetect and autoconfigure only" - in which case, if two dont work (but should), then ensure that all IRQ conflicts related to both are removed. On some occasions, one also also needs to go into the BIOS and select "Non Plug-and-Play OS" so that resource assignments are done - manually setting IRQs (where possible) is a good step as well.