Phantom Drive After Ext. Drive Removed

I’m running Win 98SE with an Adaptec 2940U SCSI adaptor for my second hard drive (D:), CD ROM drive (R:) and two Syquest removable media external drives. (E:, F:). I have since removed one of the Syquest drives, yet the drive letter remains. Properties in Windows File Manager of the Phantom drive show 0 bytes and I get a disk error if I try to access it. I removed the drive through Device Manager before detaching it from the system to no avail. How can I delete this bad drive letter?