FAT32 Drive Readable, but not Writable - GPS Device


I'm working with a new GPS/Navigation device, the Lowrance iWAY 500C. It has an internal hard drive, which you can connect to via USB. On my Mac Mini, running Mac OSX 10.3.9, it can read the hard drive on the iWAY, but it cannot write to it. If I check the drive info, it reports back as being a nonwriteable FAT32. I thought Mac OSX 10.3 and newer was read/write capable on FAT32 drives. The only problem that I have found is when I use the Disk Utility and verify the partition, it says:
"Free space in FSInfo block (1226944) not correct (1280787)
fix? no"

I know that the iWAY actually has a 20GB internal hard drive, but is partitioned into two 10GB partitions - one is read-writeable for storing MP3s and Skin files; the other is a hidden partition for storing the mapping/navigation data. I know the writeable partition works on a PC. I have also had a friend test on his G4, and he gets the same issue as me - nonwriteable FAT32 drive. And as I said, it mounts and reads completely fine.

Any ideas why a FAT32 drive would not be writeable on a Mac, but be writeable on a PC? Many thanks.