I would suspect an issue too, sooner or later. Use on PS3, Mac, and PC, see, what I'm getting at here. On top of all that you have a full partition already, right. I suggest you have 1 partition period on the ext. HD and make that Fat32 and be done from the PC. I also suggest you use the HP USB formatter which seems to handle most USB based drives. There simply maybe too much expected or going here and a fresh start maybe best to start again and retry.
I have an external hard drive full of data, and wanted one of my partitions to be usable on my PS3 so I formatted the partition to FAT32.
Now, when I plug the drive into my PS3 the partition's detected no problem, when I plug it into my fiancee's Mac they both come up, but when I plug it into my PC it just comes up as (G:) Local Disc and tells me I have to format it before I can use it.
Is there any way I can remedy this situation?