[Exim] frozen messages

I have set up EXIM so that it spools all mail from a LAN using queue_remote_smtp or something like that. Crontab dials out at specified times and runs ppp-go which in turn does a sendmail -qf (ie EXIM symlink) in ip-up.
I have set my 'configure' to route all outbound messages to my ISP's mail server. Everything worked fine for a day, but I then noticed that all the messages were being frozen. I now have to do a sendmail -qff to force delivery of frozen messages which I don't like.
In exim_mainlog the only suspicious thing is 'route append'. Should the routing section contain only my driver to send all remote mail to my ISP server?