When you have inserted the card, what does linux report about the filesystem etc? right-click the volume in konqueror, go to properties and it should tell you more. You do use KDE and not gnome, right?
Also, when you plug it in (make sure you switch it to read-only, do a dmesg, check if there are any errors. If there are none, check the partition. dmesg will report the device/partition name, something like /dev/sdc, once you have that do:
fsck -NV /dev/sdc1
What does fsck report? -N means that he will only perform a dry run, won't change anything on the device. V is for verbose ...