Hi :-)
Don't panic, take a big breath of air and try this :
1 : make a copy of your OS3.1 Workbench disk,
2 : make some room on the copy by erasing utilities drawer contents,
3 : copy Extras3.1:l/cdfilesystem to your workbench3.1:l drawer,
4 : copy Storage3.1:DOSDrivers/CD0 and CD0.info to you workbench3.1:devs/dosdrivers/ drawer,
5 : set your CDRom Drive to unit 4 with it's jumpers (see top of the drive for proper jumper settings)
6 : edit the CD0 file as follow :
FileSystem = L:CDFileSystem
Device = gvpscsi.device
Unit = 4
Flags = 0
Surfaces = 1
SectorsPerTrack = 1
SectorSize = 2048
Mask = 0x7ffffffe
MaxTransfer = 0x100000
Reserved = 0
Interleave = 0
LowCyl = 0
HighCyl = 0
Buffers = 5
BufMemType = 0
StackSize = 1000
Priority = 10
GlobVec = -1
DosType = 0x43443031
7 : save edited CD0 file back to disk ;-)
8 : edit the CD0.info tooltypes to remove DEVICE= and UNIT= entries, as usually it don't want to work as is ;-)
9 : reboot your A4000, pray a little :-D
10 : enjoy
You can now install OS3.9 with no soucy :-)
Amigalement,
Jean-François.