Thanks Pete and Thomas,
Using os2cdrom unfortunately does not change the deal with or without USB drivers declared.
Yes, if USB is set I also set the USB Cd install flag through own values choice.
In the resulting config.sys file, line 94 is :
DEVICE=\OS2CDROM.DMD /V
Note that LOCATECD.SYS is called using the same syntax:
DEVICE=\LOCATECD.SYS "Insert eComStation Installation CD-ROM and press any key." "ECS_CDRUN" "\ECS\ECS_INST.FLG"
So the error message is from LOCATECD.SYS which seems unable to know where the USB CD drive is.
Moreover at the beginning of the config.sys file, one read :
RUN=\OS2\ACPIDAEMON.EXE
but here I got no problem, the daemon is launched.
BTW where is LOCATECD.SYS on the CD ? I cannot find it.