wl300g & wl138g incompatible?

have a 300g for some time now. Works great with my laptop (wl100g). But not with a wl138g!! if i get connection it's 1mbit even while the ap is a few inches away.
so i returned the wl138g and bought an edimax. that worked, but now i needed another pci card. it's been more than a year since the wl138g problem, so i figured is must be a faulty card i got or the defect is fixed. but the new wl138 i bought today has the same problems!!
wtf is wrong???
i had other laptops and cards that connected just fine to the wl300g....

incompatability wl300g <> wl138g?