Problem Transfering from Mac to an External IDE HDD

My friend borrowed my external HDD, I use it regularly to backup my PC,and I know it worked just before I gave it to her.

While she was able to get files from my drive, she couldn't copy anything to it for me. She got an "error" saying the drive was "Protected"

She tried to copy some files from her MacBook to my external HDD. What I don't understand is why she would get that error message, if it was working fine my PC.

I don't have the drive with me...yet.

Any ideas..I'm not familiar w/the new Mac OS and compatibility issues.

Is the drive formatted with FAT or NTFS? Format it as FAT (MS-DOS File System as it is called in OS X's Disk Utility application) and you will be able to write files to it from both the Mac and PC.

I will have to check...I believe the drive is formatted as NTFS.

If it's NTFS..you can bring files over to it from a Mac??

I cannot re-format it, it has too much info on it.