Verbatim USB 8GB file copy problem

I have a 8 gb Verbatim USB  drive and copied files from Windows XP Fat32 file format on one computer to store on another computer running Windows XP NTSC format..  (Same computer manufacturer), Prior to the exercise the machine designating the VUSB drive as F: had no issues with the drive. Putting the drive in machine that began calling VUSB E: also saw all the files on drive. The files showed they were being copied to the E: drive  but when I went to transfer them back to the machine calling it F:  it saw the drive as E: and wants to reformat it.. How can the drive designation be put back to F: and files used.. Now they can only be read on one machine.. Of course the wrong one !!