[Asterisk-Users] "System" command causes core dump Warning: Newbie help :)

[Asterisk]

With the following program:

#!/bin/sh
# mailfax: program to email received fax as pdf

FAXFILE=$1
RECIPIENT=$2
FAXSENDER=$3
FAXID=`basename $1|cut -d "." -f1,2`.pdf
FAXTXT=`basename $1|cut -d "." -f1,2`.txt

tiff2pdf $FAXFILE > $FAXID

sendfax.pl $FAXID $RECIPIENT $FAXSENDER $FAXFILE
#end of program

If I execute the following from the command line:

mailfax /var/spool/asterisk/fax/1108470308.13060.tif 
somebody at company.co.uk 0178933333

everything works just fine, and the .pdf comes through as an email 
attachment

If I execute the following from the dialplan (* is CVS-HEAD 02/02/05)

exten => 666,1,System(mailfax 
/var/spool/asterisk/fax/1108470308.13060.tif somebody at company.co.uk 
0178933333)

then the tiff2pdf program generates a core dump.

Why would this be the case ? What can I start looking for ?

Julian