Message Oracle PLS-00102 - parser stack overflow because nesting is too deep

ERRORparser stack overflow because nesting is too deep
CAUSEThe parser, which checks the syntax of PL/SQL statements, uses a data structure called a stack; the number of levels of nesting in the PL/SQL block exceeded the stack capacity.
ACTIONReorganize the block structure to avoid nesting at too deep a level. For example, move the lowest-level sub-block to a higher level.