Pascal - 是什么导致了这个运行时错误 (216)?

Pascal - Whats causing this runtime error(216)?

每当我 运行 SafteyDepositBox.SetNewCode 我得到一个 runtime error 216。知道是什么原因造成的吗? 这是错误:

Runtime error 216 at [=13=]401EFC
[=13=]401EFC
[=13=]40153D

[=13=]401596
[=13=]406E31

program Boxy;
{$MODE OBJFPC}
{$M+}
type
 SDB = class
  private
   State : string;
   Code : string;
  public
   Constructor Create();
   procedure SetNewCode(newcode:string);
   function Valid(s:string):boolean;
end;

constructor SDB.Create();
begin
 State := 'Open-NoCode';
 Code := ''; 
end;

procedure SDB.SetNewCode(newcode:string);
begin
 Code := newcode;
 writeln(Code);
end;

function SDB.Valid(s:string):boolean;
var
 IsValid : boolean;
begin 
 If (length(s) = 4) then
  IsValid := true
 else
  IsValid := false;
 Valid := IsValid;
end;

var 
 SafetyDepositBox : SDB;
begin
 SafetyDepositBox.Create();
 SafetyDepositBox.SetNewCode('r2d2');// runtime error 216 here
end.

天哪,你让我想起了 Pascal!

这是调用对象构造函数的方式:

SafetyDepositBox := SDB.Create();