How can we declare and address pointer of this structure

public struct PASSTHRU_MSG
{
unsafe public System.Int32 ProtocolID;
unsafe public System.Int32 RxStatus;
unsafe public System.Int32 TxFlags;
unsafe public System.Int32 Timestamp;
unsafe public System.Int32 DataSize;
unsafe public System.Int32 ExtraDataIndex;
unsafe public System.Byte[] Data;
}

where Data is fixed array of 4000 bytes
When I try
unsafe
{
PASSTHRU_MSG1* test;
test = &ptrMsg;
}

It gives error
Error 1 Cannot take the address of, get the size of, or declare a pointer to a managed type ('project.Form1.PASSTHRU_MSG1')