Although I can still access the CF card from the camera, I can take pictures and browse them. It's just that the mac can't mount the CF card anymore (I can read other cards). The same card was working fine before the formatting.
The very weird thing is that I can't see the CF card anywhere (not in /Volumes, not in Disk Utility) and same thing happens if I try to read the CF card by connecting the camera with the USB cable. But still I can see the content of the CF card from the camera browser. The card is a Sandisk Ultra II (2GB). And this happens since I've formatted the card from the 300D with the UnDutchables Firmware.
I have tried reading the card with a PC and I got the same result, Windows show the drive letter but throws an error if I try to open the disk.
I have also tried the same process with a different CF card and I got the same result (I can't access the CF card anymore).