DIIOP security and access

We have a CLP program running on our iSeries that calls a Java program
that composes and sends emails through our Domino server. The CLP reads a
PF that contains the server name and a user name and password for
authentication to the Domino server. The contents of the emails are in
other PF's that are read by the Java program.

The Java program uses Domino classes to compose the email and DIIOP to
communicate with the Domino server and send the email.

This is something that has been working for 5+ years with no interaction
on anyone's part. Last week it decided to stop working. Only message in
the log file is: "DIIOP: user xxxxxxxx cannot access server", where
xxxxxxx is the short name of the user defined in the PF. This has been
the same user name that has worked for 5+ years and is not an actual
person who interacts with the Domino server.

The user certificate will not expire for another 10 years, the user
internet password works fine. No upgrades or PTF's were loaded on the
iSeries or Domino when it stopped working.

Any suggestions on what else to look at ? Any suggestions on how to
increase the logging level for DIIOP ?

V6R1, latest CUM. Domino 8.5.1 FP1.

Thanks in advance,
Bob Laing