ORA-01041: internal error. hostdef extension doesn't exist

Good Morning!!
Hope every one is doing a great.

I have an issue. on windows server for Oracle 10g when I try to startup the database after a shutdown, or when using RMAN when I try connecting as target database it gives me the error as hostdef does not exists.

I did a clean shut of the db.

SQL> SHUT IMMEDIATE
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> STARTUP
ORA-01041: internal error. hostdef extension doesn't exist  then I exit the session and try connecting it get connected to idle state. Later when I again try given startup mount or startup. It throws the error but after the issue of the startup command when u exit the session and try connect and check the open state of the database it show read write. This is very strange situation. Please advise any change required to fix this bug or it is a bug.

Thanks
Nilesh
/as sysdba

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