Message Oracle PLS-00313 - string not declared in this scope

ERRORstring not declared in this scope
CAUSEThere is no declaration for the given identifier within the scope of reference. The identifier might be misspelled, its declaration might be faulty, or the declaration might be placed incorrectly in the block structure.
ACTIONCheck the spelling and declaration of the identifier. Also confirm that the declaration is placed correctly in the block structure.