Delphi String Variable not same from C# String

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C#

Delphi

My Delphi Procedure is:

procedure seturunAdiGonder(_urunAdi: string); stdcall;
begin
  urunAdiGonder(Terazi, _urunAdi);
end;

And my C# Code:

 [DllImport("UcgeBizerbaScale.dll",
                   CallingConvention = CallingConvention.StdCall,
                   CharSet = CharSet.Ansi)]
        public static extern void seturunAdiGonder(string ad);

string a = textBox1.Text;
            seturunAdiGonder(a);

when i use c# code i got an error "Unhandled exception has occured in your application.If you click Continue,the application ignore this error and attemot to continue.If you click quit,the application will close immediately

Attempted to read or write protected memory.This is often an indication that other memory is currupt.".

Detail Part:"
See the end of this message for details on invoking
just-in-time (JIT) debugging instead of this dialog box.

************** Exception Text **************
System.AccessViolationException: Attempted to read or write protected memory. This is often an indication that other memory is corrupt.
at WindowsFormsApplication1.Form1.seturunAdiGonder(String ad)
at WindowsFormsApplication1.Form1.button4_Click(Object sender, EventArgs e)
at System.Windows.Forms.Control.OnClick(EventArgs e)
at System.Windows.Forms.Button.OnClick(EventArgs e)
at System.Windows.Forms.Button.OnMouseUp(MouseEventArgs mevent)
at System.Windows.Forms.Control.WmMouseUp(Message& m, MouseButtons button, Int32 clicks)
at System.Windows.Forms.Control.WndProc(Message& m)
at System.Windows.Forms.ButtonBase.WndProc(Message& m)
at System.Windows.Forms.Button.WndProc(Message& m)
at System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m)
at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)
at System.Windows.Forms.NativeWindow.Callback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)


************** Loaded Assemblies **************
mscorlib
Assembly Version: 2.0.0.0
Win32 Version: 2.0.50727.3607 (GDR.050727-3600)
CodeBase: file:///c:/Windows/Microsoft.NET/Framework/v2.0.50727/mscorlib.dll
----------------------------------------
WindowsFormsApplication1
Assembly Version: 1.0.0.0
Win32 Version: 1.0.0.0
CodeBase: file:///D:/Debug/WindowsFormsApplication1.exe
----------------------------------------
System.Windows.Forms
Assembly Version: 2.0.0.0
Win32 Version: 2.0.50727.3053 (netfxsp.050727-3000)
CodeBase: file:///C:/Windows/assembly/GAC_MSIL/System.Windows.Forms/2.0.0.0__b77a5c561934e089/System.Windows.Forms.dll
----------------------------------------
System
Assembly Version: 2.0.0.0
Win32 Version: 2.0.50727.3614 (GDR.050727-3600)
CodeBase: file:///C:/Windows/assembly/GAC_MSIL/System/2.0.0.0__b77a5c561934e089/System.dll
----------------------------------------
System.Drawing
Assembly Version: 2.0.0.0
Win32 Version: 2.0.50727.3053 (netfxsp.050727-3000)
CodeBase: file:///C:/Windows/assembly/GAC_MSIL/System.Drawing/2.0.0.0__b03f5f7f11d50a3a/System.Drawing.dll
----------------------------------------

************** JIT Debugging **************
To enable just-in-time (JIT) debugging, the .config file for this
application or computer (machine.config) must have the
jitDebugging value set in the system.windows.forms section.
The application must also be compiled with debugging
enabled.

For example:

<configuration>
<system.windows.forms jitdebugging="true">


When JIT debugging is enabled, any unhandled exception
will be sent to the JIT debugger registered on the computer
rather than be handled by this dialog box.".

can anybody help me?

Thanks