C# Fatal Execution Engine Error calling dynamically loaded .dll

Question

i started programming in c# a couple of weeks ago (coming from mostly java) and i am currenty struggling using the libMPSSE.dll library.

Here is how i import the functions:

        [DllImportAttribute("libMPSSE.dll", EntryPoint = "I2C_GetNumChannels", CallingConvention = CallingConvention.Cdecl)]
    public static extern uint I2C_GetNumChannels(ref uint NumChannels);

    [DllImportAttribute("libMPSSE.dll", EntryPoint = "I2C_OpenChannel", CallingConvention = CallingConvention.Cdecl)]
    public static extern uint I2C_OpenChannel(uint index, ref IntPtr handler);

    [DllImportAttribute("libMPSSE.dll", EntryPoint = "I2C_GetChannelInfo", CallingConvention = CallingConvention.Cdecl)]
    private static extern uint I2C_GetChannelInfo(uint index, ref FT_DEVICE_LIST_INFO_NODE chanInfo); 

And this is what the C++ header file in the .dll looks like:

FTDI_API FT_STATUS I2C_GetNumChannels(uint32 *numChannels);
FTDI_API FT_STATUS I2C_GetChannelInfo(uint32 index, FT_DEVICE_LIST_INFO_NODE *chanInfo);
FTDI_API FT_STATUS I2C_OpenChannel(uint32 index, FT_HANDLE *handle);

The first two run fine, but if i call the third one i get the FatalExecutionEngineError:

       for (uint i = ch; i >= 0; i--) { //ch contains number of chans available

            FT_DEVICE_LIST_INFO_NODE nodeInfo = new FT_DEVICE_LIST_INFO_NODE();

            I2C_GetChannelInfo(i, ref nodeInfo); // crash here
            Console.WriteLine(" > info: "+nodeInfo.Description);

            }
        } 

I guess the crash is cause by the FT_DEVICE_LIST_INFO_NODE parameter, which looks like this in my code:

    public class FT_DEVICE_LIST_INFO_NODE
    {
        public UInt32 Flags;
        public FTDI.FT_DEVICE Type;
        public UInt32 ID;
        public UInt32 LocId;

        [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 16)]
        public string SerialNumber;

        [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 64)]
        public string Description;

        public IntPtr ftHandle;
    }

And according to the .dll documentation, looks like this in c++ code:

typedef struct _ft_device_list_info_node {
    DWORD Flags;
    DWORD Type;
    DWORD ID;
    DWORD LocId;
    char SerialNumber[16];
    char Description[64];
    FT_HANDLE ftHandle;
} FT_DEVICE_LIST_INFO_NODE;

I am kinda lost right now and just try and error without really knowing how to fix this problem, certainly doesnt help that is my first time using an unmanaged .dll :D

The lib can be found here http://www.ftdichip.com/Support/SoftwareExamples/MPSSE/LibMPSSE-I2C.htm with documentation available here http://www.ftdichip.com/Support/Documents/AppNotes/AN_177_User_Guide_For_LibMPSSE-I2C.pdf

Thanks in advance

/edit: i forgot the FT_DEVICE enum

        public enum FT_DEVICE
    {
        /// <summary>
        /// FT232B or FT245B device
        /// </summary>
        FT_DEVICE_BM = 0,
        /// <summary>
        /// FT8U232AM or FT8U245AM device
        /// </summary>
        FT_DEVICE_AM,
        /// <summary>
        /// FT8U100AX device
        /// </summary>
        FT_DEVICE_100AX,
        /// <summary>
        /// Unknown device
        /// </summary>
        FT_DEVICE_UNKNOWN,
        /// <summary>
        /// FT2232 device
        /// </summary>
        FT_DEVICE_2232,
        /// <summary>
        /// FT232R or FT245R device
        /// </summary>
        FT_DEVICE_232R,
        /// <summary>
        /// FT2232H device
        /// </summary>
        FT_DEVICE_2232H,
        /// <summary>
        /// FT4232H device
        /// </summary>
        FT_DEVICE_4232H,
        /// <summary>
        /// FT232H device
        /// </summary>
        FT_DEVICE_232H,
        /// <summary>
        /// FT232X device
        /// </summary>
        FT_DEVICE_X_SERIES
    };

Answer 1

Thanky you everone, i got it running now. I made a struct out of FT_DEVICE_LIST_INFO_NODE and added LayoutKind.Sequential and CharSet.Ansi attribute. I also changed FTDI.FT_DEVICE to a simple uint for test purpose and it seems to run now.

    [StructLayoutAttribute(LayoutKind.Sequential, CharSet = CharSet.Ansi)]
    public struct FT_DEVICE_LIST_INFO_NODE
    {


        public uint Flags;
        public uint Type;
        public uint ID;
        public uint LocId;

        /// char[16]
        [MarshalAsAttribute(UnmanagedType.ByValTStr, SizeConst = 16)]
        public string SerialNumber;

        /// char[64]
        [MarshalAsAttribute(UnmanagedType.ByValTStr, SizeConst = 64)]
        public string Description;
    }