Incompatible types: 'String' and 'procedure, untyped pointer or untyped pa...

Jeg har lavet en DLL fil med en række forskellige funktioner.
Når jeg prøver at kalde en bestemt en siger den: "Incompatible types: 'String' and 'procedure, untyped pointer or untyped parameter'"
... hvad gør jeg galt?

Kode 

library DLL;

uses
  ShareMem,  
  SysUtils,
  Classes,
  Windows;

{$R *.res}

function SysTempPath: string; stdcall; 
var
  buffer: array[0..1023] of char;
begin
  SetString(Result, Buffer, GetTempPath(Sizeof(Buffer) - 1, Buffer));
end;

exports SysTempPath;

end.

Kode 

unit fProject;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls;

type
  TProjectForm = class(TForm)
    Button: TButton;
    procedure ButtonClick(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  ProjectForm: TProjectForm;

  function SysTempPath: string; stdcall; external 'DLL.dll'

implementation

{$R *.dfm}

procedure TProjectForm.ButtonClick(Sender: TObject);
begin
  ShowMessage(
    SysTempPath
  );
end;

end.

Kode 

program Project;

uses
  ShareMem,
  Forms,
  fProject in 'fProject.pas' {ProjectForm};

{$R *.res}

begin
  Application.Initialize;
  Application.CreateForm(TProjectForm, ProjectForm);
  Application.Run;
end.

Prøv at ændre resultattypen af funktionen fra string til pchar.