using CONFIG to set GISBASE

[James McManus]

I am getting the following error message when I try and read a grass 
vector file:

msDrawMap(): Image handling error. Failed to draw layer named 'roads'.
msOGRFileNextShape(): OGR error. Cannot open database dbf by driver 
/var/www/html/mapserver/grassdata/MDI/PERMANENT/dbf/, check if GISBASE 
environment variable is set, the driver is available and the database is 
accessible.

I been trying to set GISBASE using the CONFIG keyword in my .map file:

NAME "MDI"
UNITS DD
EXTENT -68.40 44.23 -68.23 44.39
SIZE 640 480
IMAGECOLOR 189 202 222
IMAGETYPE PNG
CONFIG "GISBASE" "/usr/local/grass-6.2.0/"

I have tried variations, such as not using quotes, but no success so 
far. How is this done? I'm using mapserver 4.10, so the CONFIG keyword 
should be available.

Jim