Could not Connect to 8.1.6

[N J Neog]

Hi all,   We 3 Oracle server as follows.   A. Oracle8 Enterprise Edition 8.0.5 B. Oracle8i Enterprise Edition 8.1.5 C. Oracle8i Enterprise Edition 8.1.6 was Installed Recently.   All are in Digital Unix   The problem is    From a Unix user if my ORACLE_HOME is pointing to database A(8.0.5) or B(8.1.5), we can connect from Sqlplus to Oracle Server A and B not to C (8.1.6.) But If ORACLE_HOME is pointing to C(8.1.6), Sql Plus can connect to all database.     Is there a problem with 8.1.6 ? or had we Installed 8.1.6 wrongly ? Any suggestion how to rectify it assuming my ORACLE_HOME always points to 8.1.5 or 8.0.5.   Thanks in advance   Regards.   Naba J Neog