MPC doesn't recognize CF disk

I put my CF disk in my MPC, connected it to my PC via usb and that works fine. The PC sees the disk, am able to copy files to the disk without any strange errors or a really slow speed or something. But once I try to load the disk in the MPC it says theres no disk inserted? Anyone had this problem as well? I haven't tried out other disks yet as this one is pretty new and seems to work

I didn't think about that being a possible solution, tried it now but does not seem to help... The required format is FAT32 right?

EDIT:
After searching for a while I managed to fix the problem! First format FAT32 and then install jjos through this guide: http://www7a.biglobe.ne.jp/~mpc1000/update308.htm