Simulink S function using a C++ code with commercial .dll files

[James]

Hello,
I am creating an S function in simulink using the legacy code generator.
My C++ source code will compile and work by itself without any issues.
This C++ code imports functions from an external dll file.
I do not have a .lib or .h file for this dll library, it is commercial library.
So I import the functions using this method:

static HINSTANCE hGetProcIDDLL = LoadLibrary("\TheFile.dll");
FARPROC lpfnGetProcessID = GetProcAddress(HMODULE (hGetProcIDDLL),"OPT");
typedef int (__stdcall * pICFUNC2)(char*);
pICFUNC2 OPT;
OPT = pICFUNC2(lpfnGetProcessID);

I can compile the s function without errors. However, when I go to run it, I get a segmentation fault (matlab freezes up and closes with no error messages given).
If I take out the calls to the imported functions in the C++ code, everything runs fine.

extra info:
-my matlab C++ compiler is set as Visual Studios 2010
-This is what my s-function legacy code looks like, it may have some unnecessary stuff:
clc
clear
def = legacy_code('initialize')
def.Options.language = 'C++';
def.OutputFcnSpec=['double y1 = positionfunct(void)']
def.IncPaths = {'C:\mtlb11b\bin\s function block'}
def.SrcPaths = {'C:\mtlb11b\bin\s function block'}
def.LibPaths = {'C:\mtlb11b\bin\s function block'}
def.HeaderFiles = {'Sfile.h','windows.h'}
def.SourceFiles = {'CodeForSFile.cpp'}
def.SFunctionName = 'GetPosition'
def.HostLibFiles = {}
def.TargetLibFiles = {'PCI_VME.lib'}
legacy_code('sfcn_cmex_generate',def)
legacy_code('compile',def)
legacy_code('Slblock_generate',def)
legacy_code('sfcn_tlc_generate',def)
def.SampleTime = 'parameterized'

If anyone has any advice regarding this, I would greatly appreciate it.

James