Pro*C problem with sqlglm()

We are having a problem with Pro*C programs running on a client and accessing a remote Oracle7 server. sqlglm() is never able to return the error message. It always outputs messages of the folowing kind:

ORA-12571: Unable to open message file (SQL-02113).

The client has only the following products installed Pro*C 2.0, SQL*Net V2, SQL*Plus. All the mesg directories and message files seem to be there. oerr ORA 12571 works fine and the relevant message file tnsus.msg is available.
What's going on here?

dave

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David-Michael Lincke	Institute for Information Management at USG
EMail: dlincke_at_sgcl1.unisg.ch
URL: http://www-iwi.unisg.ch/about/team/dal.html