Oracle Message PLS-00368 - in RAISE statement, string must be an exception name

ERRORin RAISE statement, string must be an exception name
CAUSEThe identifier in a RAISE statement is not a valid exception name.
ACTIONMake sure the identifier in the RAISE statement was declared as an exception and is correctly placed in the block structure. If you are using the name of a PL/SQL predefined exception, check its spelling.