Both Win 95 and 98 have had phantom drive bugs. Which OS is this? Check out Config.sys: If it has a line in there "LASTDRIVE=Z", then change the letter designator to the actual "number" of drives there are in the system. (i.e. floppy, one hard drive and a CD, then LASTDRIVE=D). This helps prevent Windows from assigning a phantom drive. If the line ISN'T there, then Windows will automatically set the Lastdrive to equal "Z", then sometimes that allows that phantom bug to pop up.
You could also try this: In Config.sys, there may be a line there...."BUFFERS=12,0"...if that second number is anything other than "0", that could be the cause of the problem...reset it to "0".