oracle error- ORA-00024: logins from more than one process not allowed in single-process mode

ORA-00024: logins from more than one process not allowed in single-process mode

Cause:     Trying to login more than once from  different processes for ORACLE started in
single-process mode.

Action:     Logoff from the other process.

oracle error- ORA-00023: session references process private memory; cannot detach session

ORA-00023: session references process private memory; cannot detach session

Cause: An attempt was made to detach the current session when it contains references to
process private memory.

Action: A session may contain references to process memory (PGA) if it has an
open network connection, a very large context area, or operating system privileges. To allow
the detach, it may be necessary to close the session's database links and/or cursors.
Detaching a session with operating system privileges is always disallowed.

ORA-00022: invalid session ID; access denied

ORA-00022: invalid session ID; access denied

Cause:     Either the session specified does not exist or the caller does not have the privilege
to access it.

Action:     Specify a valid session ID that you have privilege to access, that is either
you own it or you have the CHANGE_USER privilege.