MS-DOS/MSCDEX wierdness

I have a PC used (or at least intended) for floppy transfers, which has a hard drive booting MS-DOS 6.22, with an 80-track 5.25" drive and a 3.5" drive connected to a WDAT-240 controller. It has the MS-DOS network stuff installed so I can connect to a shared network drive. It's also got a CDROM drive on its second IDE bus, and the corresponding lines for the driver and MSCDEX are in CONFIG.SYS and AUTOEXEC.BAT. Most of the drivers etc are loaded in high memory (I ran MEMMAKER in the dim and distant past). At the moment, those two lines are commented out because if they're not, the floppies don't work properly. Has anyone got any idea why? The CDROM works fine if I uncomment those lines (but the floppies don't) and network shares work fine either way. -- Pete Peter Turnbull Network Manager University of York