Cause: In a reference to a component
(for example, in the name A.B, B is a component of A), the component has
not been declared. The component might be misspelled, its declaration might be
faulty, or the declaration might be placed incorrectly in the block
structure.
Action: Check the spelling and
declaration of the component. Also confirm that the declaration is placed
correctly in the block structure.

Relared Errors:
PLS-00303:
qualifier `string` must be declared
PLS-00304:
cannot compile body of `string` without its
specification
PLS-00305:
previous use of `string` (at line string) conflicts with
this use
PLS-00306:
wrong number or types of arguments in call to
`string`
PLS-00307: too
many declarations of `string` match this call
PLS-00308: this
construct is not allowed as the origin of an assignment
PLS-00309: with
%%LAST attribute, `string` must be a variable of an enumerated
type
PLS-00310: with
%%ROWTYPE attribute, `string` must name a table, cursor or
cursor-var
PLS-00311: the
declaration of string is incomplete or malformed
PLS-00312: a
positional parameter association may not follow a named
association