If you have an ISA AdLib I/O card in your system to extend the number of available serial/parallel ports but have difficulties getting its ports recognized in BeOS, try removing /system/add-ons/kernel/busses/ide/ pcmcia. On a desktop system, I’d wager you won’t have PCMCIA anyway. After this, you can use the Devices preferences panel to add the ports.
Note that it has only been since R5 that the conflict between /system/add-ons/kernel/busses/ide/pcmcia and the card arose, and it is still present in 5.0.3.