Suddenly my 1tb western hdd is telling me my file limit is 4gb??

I've had a 1tb western digital hard drive for over a year. In which time I've used it to capture hours upon hours of hdv footage through fcp on my old macbook, with out any problems.

However I have recently bought a brand new imac and when I tried to set the same hdd as my scratch disk, in fcp, a msg comes up saying "The selected disk is formatted using FAT32 which has a 4gb file size limit." And sure enough when i try to copy a file which has a size greater than 4gb on to the drive "the operation can't be completed because an unexpected error occured (error code 0)" pops up!!

If any one can give a solution and an explanation as to how this has happened it would be greatly appreciated.

Thanks in advance

cheers for the replies guys.

the drive is formatted to MS-DOS (FAT32). Its not just a fcp error because I've tried copying large files from my mac hdd on to the external with no luck.

I'm going to try reformatting the drive now, I'll let you know how I get on. I don't suppose any one can tell me how the drives format changed by simply connecting it to a new imac??

I'm not sure what format the HDD was in before but used it to store huge fcp files, plus many other files from my macbook and the macpros at my uni for well over a year. All I did was plug it in to my new imac and it appears to have changed the format with out deleting or corrupting any of the files on it?!

I've formatted it to Mac OS Extended (Journal) now and it's working fine. Thanks for the help everyone.