Cheat Engine

[IIZoom%]

Hi, I'm trying to inject this function:

extern "C" TEST void Mfunc(void* stru)
{
Data* msg = (Data*)stru;

if (!msg)
return (MessageBoxA(NULL, "NULL", "NULL", MB_OK), (void)0);

std::string itemHandle = msg->m_vecData.at(0)._handle + "\t";
MessageBoxA(NULL, itemHandle.c_str(), itemHandle.c_str(), MB_OK);
return;
}

Basically, I'll take a pointer to a struct and modify its content. The struct in the original code is created on the stack, if that makes any difference.

I want to inject this code before another function that takes the same reference. Here is the code I have:
lea esi,[esp+1C]
diealy call my function here
call 006E4D00

So I created an Auto Assembler script like this:
lea esi,[esp+1C]
pushad
pushfd
push esi
call Mfunc
pop eax
popfd
popad
call 006E4D00
jmp return

But it crashes the game every time it is called. The message boxes do appear, though.

i just need to know what i might be doing wrond, thank you