having exactly the same problem - thought i would bump this. i once read a detailed post on exactly what to do to get this card working - wish i had bookmarked it cause it was really helpful. not sure if it was on this site or another.
I'm using a microsd card, a minisd adapter and I'm using this
version of the EZ Flash IV cart.
I used this thread to set my cart up without a hitch.
Link to the thread.
I used the files found on the official site here
to set my cart up though since the links used in the thread mention above were out of date.
One thing it doesn't mention though it is best not to patch the reset function onto the roms.
Just turn it off and back on a couple seconds later if you want to change games.
Some games will not work I've found if you patch the cheats
Only thing left that I'm working on is a couple games not saving.
Probable have the wrong save auto selected by the client or they need a patch.
I'll figure it out eventually and post back.
Edit: Using the SRAM Patcher in gbata fixs some games that don't save properly after the client patches them. Just remember to patch them again with the client.
If your still having problem afterwords post back with the most detail you can.