导入C dll函数到c#

这是我的第一篇stackoverflow帖子。这个问题我已经纠结了好几天了。我尝试导入usbi2cio.dll，这是一个C Dll到一个基于c#的项目。我浏览了网站上大多数类似的帖子，但我仍然无法解决我的问题，因为我的情况可能有点不同。

LONG _stdcall DAPI_ReadI2c(HANDLE hDevInstance, I2C_TRANS * TransI2C);
typedef struct _I2C_TRANS {
    BYTE byTransType;
    BYTE bySlvDevAddr;
    WORD wMemoryAddr;
    WORD wCount;
    BYTE Data[256];
}I2C_TRANS, *PI2C_TRANS;
//In my C# code, I did the translation like this:
[StructLayoutAttribute(LayoutKind.Sequential), Serializable]
public struct I2C_TRANS
{
    public byte byTransType;
    public byte bySlvDevAddr;
    public ushort wMemoryAddr;
    public ushort wCount;
    [MarshalAsAttribute(UnmanagedType.ByValArray, SizeConst = 256, ArraySubType = UnmanagedType.I1)]
    public byte[] Data;
    public I2C_TRANS(int size)
    {
        Data = new byte[size];
        this.byTransType = 0x00;
        this.bySlvDevAddr = 0x00;
        this.wMemoryAddr = 0;
        this.wCount = 0;
    }
};
public I2C_TRANS TransI2C = new I2C_TRANS(256);
public IntPtr[] hDevice = new IntPtr[DAPI_MAX_DEVICES];
...
TransI2C.byTransType = byTransType;
TransI2C.bySlvDevAddr = bySlvDevAddr;
TransI2C.wMemoryAddr = wMemoryAddr;
TransI2C.wCount = wCount;// no larger than 64
...
if((hDevice[0] = DAPI_OpenDeviceInstance(devName, 0)) != INVALID_HANDLE_VALUE)
    //the returned lReadCnt should be equal to wCount.
    Public int lReadCnt = DAPI_ReadI2c(hDevice[0], ref TransI2C);

由于某种原因，读I2C事务中的结构不能很好地传递，结果，函数返回0值而没有错误(我期望的是与wCount相同的值)。对于其他一些类似的API和结构，它工作得很好。那么这个问题的原因是什么呢?

//Here is the P/Invoke declaration:
[DllImportAttribute("UsbI2cIo.dll", EntryPoint = "DAPI_ReadI2c", CallingConvention = CallingConvention.StdCall)]
public static extern int DAPI_ReadI2c(IntPtr hDevInstance, ref I2C_TRANS TransI2C);