Oracle Solution for Error ora-09851

ORA-09851: soacon: Archmon unable to lock named pipe.

What triggered the Error:

fcntl() failed to set read lock on named pipe ?/dbs/mon2arch_@.

What should we do to fix it:

Make sure that archmon is not already active on another terminal for this ORACLE_SID. Only one archmon session is allowed at a time for a given instance.