C2028   ENDDO does not match WHILE

     Explanation:  You specified an ENDDO statement without a
     corresponding DO WHILE statement.  ENDDO is part of the DO WHILE control
     structure syntax and, therefore, cannot occur outside of the structure.
     This error may be due to improperly nested DO WHILE structures.

     Action:  Remove the offending ENDDO statement or fix the nesting
     error, and recompile.