SQL*NET error on remote connection attempt

Hi,

        I am having a problem trying to connect using SQL*Net between Oracle running on an HP 900 750 and on a SUN. I installed and set up SQL*NET on the HP, and can connect to the Oracle instance on the SUN with say:

        sqlplus /_at_t:{SUN machine}:{SUN Oracle SID}

but when I try to connect to the Oracle instance on the HP from the SUNs, I get:

SQL*Plus: Release 3.1.2.3.1 - Production on Tue Apr 19 10:59:44 1994

Copyright (c) Oracle Corporation 1979, 1992. All rights reserved.

ERROR: ORA-03113: end-of-file on communication channel

Enter user-name:

Has anybody else seen and solved this problem. I am using Oracle 7.0.15.4.0 on the SUNs and Oracle 7.0.13.1.0 on the HP. Also SQL*Net is running on both mathines

-- 
        Michael D. Grapevine 
        NSWC PHD
        Code 4G33 
        Port Hueneme, CA 93043
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