Marshalling and callback with Unmanaged dll

Hi,
I have the following structures in a C dll,

Code:

---


In C:

typedef struct Structure1
{
        SomeStruct list1;// Somestruct is a structure
        SomeStruct List2;
        SomeEnum state; // SomeEnum is a Enum
        unsigned char *pcurrent;
        unsigned short Length;
        SomeStruct addr;
        SomeStruct timer;
        unsigned short retries;
        unsigned char flag;
        unsigned short seq;
        someEnum2 Mtype;
        unsigned char action;
        unsigned int size;
        unsigned char *ptr; //data segment
}struct1;

typedef struct Structure2
{
        struct1 Msg;       
}struct2;

---

for the above structures, i have written the following structures in C#,

Code:

---

In C#:

        [StructLayout(LayoutKind.Sequential)]
        public struct struct1
        {
            public int List1;
            public int List2;
            public someenum State;
            public int pCurrent;
            public short Len;
            public int Addr;
            public int Timer;
            public ushort Retries;
            public char Flags;
            public ushort SeqNum;
            public ushort InvokeId;
            public someenum MType;
            public char Action;
            public int DataBuffSize;
            [MarshalAs(UnmanagedType.ByValArray, SizeConst = 10000)]
            public byte[] ptr;
        }

[StructLayout(LayoutKind.Sequential)]
        public struct struct2
        {
            public struct1 Msg;
        }

---

and i have the following callback function in the managedcode.

Code:

---


In C#:

public void CallBack(long hDev, ref struct2 pData);

---

This callback function is invoked by a function in unmanaged code.
I have written the following delegate for the callback function,

Code:

---


[UnmanagedFunctionPointer(CallingConvention.Cdecl)]
public delegate void CallBack_delegate(long hDev, ref struct2 pData);

public static CallBack_delegate call_del = CallBack;

---

I am getting Access violation exception when the call back funciton is executed.

pls help.