Mac OS X corrupts exFAT USB HD !?


I have an iMac 27" with Lion and Windows 7 (BootCamp).
I formated a USB 2TB HD to exFAT for compatibility with both systems.

When I boot under Mac and write data to my external drive it becomes unusable under Win7 (error 0x80071AC3 - disk damaged). I found a command : chkdsk :x /F (where x is the letter of my drive) which will temporarily fix it until I write data under Mac again...

Has anyone got any clue ?

btw I searched for exFAT and no results and I hope I'm in the right section.
Ok so the solution was to format the disk with MBR partition table (instead of GUID) but I read somewhere that MBR is limited to 2TB which just suits me in this case :eek:

I did read somewhere that GPT should be fine for Win7 and Lion...

Thank you for reading.