void ListExtensions(out int pCount, System.IntPtr pExtensions)

public struct ExtensionId
{
    public ExtensionGuid data;
}

public struct ExtensionGuid
{
    public int Data1;
    public short Data2;
    public short Data3;
    public byte[] Data4;
}

ExtensionId *ids = new ExtensionId[10];

ExtensionId[] ids = new ExtensionId[10];
GCHandle handle = GCHandle.Alloc(ids);
IntPtr ptr = (IntPtr)handle;
int pCount;
ListExtensions(out pCount, ptr);
ExtensionId[] result = (ExtensionId[])handle.Target;

The runtime has encountered a fatal error. The address of the error was at 0x73d87e37, on thread 0x5f8. The error code is 0xc0000005. This error may be a bug in the CLR or in the unsafe or non-verifiable portions of user code. Common sources of this bug include user marshaling errors for COM-interop or PInvoke, which may corrupt the stack.