This old post suggests that MAYBE (wild guess here) you inadvertantly formatted the drive such that only "root" has write permissions:
http://mandrivausers.org/index.php?/...-drive-solved/
Strong suggestion:
1. Mount the drive
2. Format the drive as FAT32 (allowing you to read and copy files on any PC, not just Linux PCs)
3. See if the problem persists with the FAT32 filesystem
Two problems with FAT32:
* You'll lose Linux permissions or the ability to do soft links (if these are critical)
<= If you're just copying "files" (especially "tar" files, which allow you to RETAIN directories and Linux permissions), there should be no problem
* You'll be limited to max filesize of 2GB
'Hope that helps .. PSM