The default card type for each PCMCIA slot is a modem card. If only one modem card is plugged in, the empty slot is ignored.
From the pcsertest Option window, you can choose to test socket I/O cards. To test a socket card, choose Socket on the Card Type switch. If you choose to test a socket I/O card in an empty slot, the test fails.
Any combination of modem and socket I/O cards can be placed in the PCMCIA slots. However, you must select the correct type of card in the Option window. If you select an incorrect card type, the test fails.