Axim X3 SD Card Compatiblity Confusion

For over a year I used a 2gb Sandisk SD card in my Axim X3 and it worked fine. Last winter I switched to a RiData 4gb cheapie 60x sd card (for which only 2 gb is recognized by my X3 and my Ipaq hx2755, the card is truly of inferior quality), moving my Sandisk 2gb to my daul-slot iPaq hx2755 which also has an 8gb CF card.

Recently I picked up a new PQI 4gb 150x sd card, which is not recognized by my Axim x3 (even when formatted in Fat16) but is recognized and works fine in my iPAQ hx2755 (all 4gb, looks like that's where it will stay). The funny part is now my Axim X3 no longer recognizes the 2gb Sandisk SD card, I previously used in it and worked just fine? I just don't know why?

Can anyone please enlighten me as to why this is happening with the sd card slot in my X3? It all seems very crazy to me, thanks!