OS : HPUX 11i
DB : 806

The problem seems to have happened all of a sudden.

We have a server running 3 databases. "oracle" is the unix user that owns oracle installation and databases. Its in "dba" group.
I log in to the server as "oracle" user, set ORACLE_SID (through oraenv) and invoke "svrmgrl". When I say "connect internal" at the "SVRMGR>" prompt, it asks for "Password:" !! I don't think this has happened ever before. The databases are running there for last 4 years. When I try any password at the "Password:" prompt, it gives me "ORA-01031" error.

So far, going through all notes and documents, I have checked following things (Metalink Note 69642.1) :
01. The "oracle" user is really still in "dba" group.
02. The "dba" group entry exists in /etc/group and exists only once.
03. The config.c file indeed has "dba" as the group definition.
04. At our site "sqlnet.ora" doesn't exist. We don't use it.
05. Permissions on all *.ora files in $TNS_ADMIN directory are "-rw-r--r--".
06. ORACLE_HOME variable is defined correctly and the path exists.
07. ORACLE_SID is set to SID of an existing database that is running fine.
08. TWO_TASK is NOT set.
09. Permissions on "oracle" executable are indeed "rwsr-s--x".
10. File systems are mounted without "nosuid" option.
11. There are no extra shared mem segments (used ipcs -b).
12. Checked with Unix SAs if anything has changed at server level. "NO".

We had changed our SYS/SYSTEM passwords last week. We suspected that as a cause but, had that been the case, the failures in "connect internal" should have happened immediately after the password change.
There is remote authentication in use. The "remote_password_file" parameter is set to "none".

Another way I tested the things was : set ORACLE_SID, ran "sqlplus /". Works fine, connects successfully. When I say "conn sys as sysdba" at the "SQL>" prompt, it fails with same ORA-1031 error.

What am I missing ? And, how could I resolve this issue ? We have quite a few cron jobs and monitoring scripts that do "connect internal" and all of them are failing.