C#中调用C++生成的dll出错，请教请教！? 400 报错

C#中调用C++生成的dll出错，请教请教！? 400 报错

在C++中生成的dll，函数定义为int CebxInitial(string inFilename)
在WPF中调用（属于C#吧），编译链接没错，运行报错：

Managed Debugging Assistant 'PInvokeStackImbalance' has detected a problem in 'E:\WPFtestCebxTools\WPFtestCebxTools\bin\Debug\WPFtestCebxTools.vshost.exe'.
Additional Information: A call to PInvoke function 'WPFtestCebxTools!WPFtestCebxTools.MainWindow::CebxInitial' has unbalanced the stack. This is likely because the managed PInvoke signature does not match the unmanaged target signature. Check that the calling convention and parameters of the PInvoke signature match the target unmanaged signature.

是不是说类型不匹配啊？我试了试，除非传空参数不报错，传string、char*都报错，就是运行到
res  = CebxInitial(namein);///////////////
这一行时报错。
是我的DllImport时参数设置不对还是其他的啊？

WPF中大致代码如下：

namespace WPFtestCebxTools
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
            ///////////////////////////
        [DllImport("CebxtoPngDll.dll", EntryPoint = "CebxInitial",
        CharSet = CharSet.Ansi,
        CallingConvention = CallingConvention.StdCall)]
        public static extern Int32  CebxInitial(String inFilename);

        public MainWindow()
        {
            InitializeComponent();

            //StringBuilder namein = new StringBuilder("D:\\test.cebx");
            string namein = "D:\\test.cebx";
            //StringBuilder nameout = new StringBuilder("D:\\test.png");
            String nameout = "D:\\test.png";
            String exfcnameout = "no exfc";

            Int32 res = 0;

            res  = CebxInitial(namein);///////////////
        }
     }
}