My company's sales reps dial in to our server on an ISDN line. Whilst
one rep is not experiencing problems, the other constantly gets the
above error.

I have checked all the settings on the server and the RAS is
functioning perfectly (hence the other rep is not getting any
trouble). I have therefore checked every last individual setting on
the rep's laptop but could find no problems. Starting to get
desperate I have talked him through deleting his DUN connection,
removing the TCP/IP stack on his machine and then re-installing it and
re-creating the DUN. It still generates the same error.

I have also been over the settings of his account on the server, and
even tried creating a new account with dial in permissions and still
the same thing still happens!

We have now got his ISDN provider running tests on the line, the
results of which are not yet known.

Is there anything I have missed?

Any help gratefully received.