Saleh:
Make sure that you do have set on the quintum the parameter End of dial digit = # so at the moment that the timer expires the system automatically will enter the # sign if the customer does not dials it, if that is not set, then the system will assume that the customer never dialed the # as this is the case, the other customers probably are dialing the # and that is why they do not have a problem, you can use this configuration example:
http://www.sysmaster.net/phpBB2/viewtopic.php?t=5
If this is not the case then I agree with the explanation of Noname.
Regards,
Saul