I'm using the original German CD's. I've definately seen that error message before but if I recall correctly I got that before I even got into the game. I think the "fix" was simply to wait for a newer version of DOSBox. So maybe you should try some other builds.
Go to http://www.si-gamer.net/gulikoza/ for gulikoza's build, also check out the older versions on that page if it still doesn't work.
And FWIW here's the full conf file I used:
[sdl]
fullscreen=true
fulldouble=true
fullfixed=true
fullresolution=1280x960
output=direct3d
hwscale=1.00
autolock=true
sensitivity=100
waitonerror=true
priority=higher,normal
mapperfile=mapper.txt
[dosbox]
language=
machine=vga
captures=E:\Apps\_Games\emulation\DOS\D-Fend 2\capture
memsize=16
[render]
frameskip=2
aspect=true
scaler=normal2x
[cpu]
core=normal
cycles=50000
cycleup=500
cycledown=500
timesynched=true
showcycles=true
[mixer]
nosound=false
rate=22050
blocksize=2048
prebuffer=10
[midi]
mpu401=false
intelligent=false
device=default
config=
[sblaster]
type=none
base=220
irq=5
dma=1
hdma=5
mixer=true
oplmode=auto
oplrate=22050
[gus]
gus=true
rate=22050
base=240
irq1=7
irq2=7
dma1=3
dma2=3
ultradir=C:\ULTRASND
[speaker]
pcspeaker=false
pcrate=22050
tandyrate=22050
disney=false
[dos]
xms=true
ems=false
[modem]
modem=false
listenport=23
comport=COM1
[directserial]
directserial=false
Comport=COM1
realport=1
defaultbps=1200
parity=N
bytesize=8
stopbit=1
[ipx]
ipx=false
[autoexec]
mount D "E:\Apps\_Games\emulation\DOS\Dosgames" -ioctl -label D
mount C "E:\Apps\_Games\emulation\DOS\Dosgames\C" -ioctl -label C
mount F "F:\" -t cdrom -ioctl -label F
F:
cd\
cd
call WC3GRAV.BAT
Good Luck.