C# wrapper for BSL430 DLL?

Has anybody done a C# wrapper for the BSL430 DLL, the DLL that controls loading of the application to the MPS430 by using its on-board BSL?

I call BSL_setFamily and BSL_setCom from C# OK which I use to set up for a USB download.

BSL_initialize_BSL is also OK.

However, something that uses the DataBlock, for example, BSL_RX_Password generates exceptions in C#.

I have the structure like this in C#:

[

StructLayout(LayoutKind.Sequential)]
public unsafe struct DataBlock
{
    public fixed byte data[10240];
    public uint numberOfBytes;
    public uint startAddr;
};

The function like this:

[

DllImport("BSL430.dll", EntryPoint = "BSL_RX_Password", CallingConvention = CallingConvention.Cdecl)]
private static extern byte BSL_RX_Password(DataBlock data);

I have tried many combinations of the structure including various "MarshallAs" and "FieldOffset" but everything I try either gives a memory use exception (reading or writing to protected memory) or a mixed managed/unmanaged exception.

Below I have given examples of two C# wrappers for DataBlock and text comments above them for the exceptions I get when using them:

// System.AccessViolationException: Attempted to read or write protected memory.
// This is often an indication that other memory is corrupt

StructLayout(LayoutKind.Sequential)]
public unsafe struct DataBlock
{
   public fixed byte data[10240];
   public uint numberOfBytes;
   public uint startAddr;
};

// Cannot marshal field 'data' of type 'DataBlock': Invalid managed/unmanaged type
// combination (this value type must be paired with Struct)

[StructLayout(LayoutKind.Explicit, Size = 10248)]
public unsafe struct DataBlock
{
    [FieldOffset(0), MarshalAs(UnmanagedType.ByValArray, SizeConst=10240)]
    public fixed byte data[10240];

    [MarshalAs(UnmanagedType.U4)]
    [FieldOffset(10240)]
    public uint numberOfBytes;

    [MarshalAs(UnmanagedType.U4)]
    [FieldOffset(10244)]
    public uint startAddr;
};

So, does anybody have a C# wrapper for this DLL API?