as _bstr_t is simply encapsulation for COM support functions (SysAllocString,
SysFreeString etc. ) You should not use these function when COM susbsystem is
(not yet or already) unavailable. What you do is:

1. initialize _bstr_t before COM is available (_bstr_t may delay call to
SysAllocString till you actually put something in it, but you are still in danger)

2. I also guess that you call CoUninitialize before _bstr_t destructor is
called. This means that when SysFreeString is called, there is no COM
sybsystem to handle your call.

What you should do is to initialize COM before you start any COM-related
activity and un-initialize when you are 100% done. Like here:

#include <cstdio>
#include <stdexcept>

#include <comdef.h>
#include <comutil.h>

int main()
{
  int result = 13;
  if (FAILED(CoInitialize(NULL)))
  {
    puts("Failed to initialize COM");
    return result;
  }

  try
  {
    _bstr_t a = "blablabla";
    // .... call your functions that use COM
    result = 0;
  }
  catch(std::exception& e)
  {
    puts(e.what());
    result = 1;
  }
  catch(_com_error e)
  {
    puts(static_cast<const char*>(e.Description()));
    result = 2;
  }

  CoUninitialize();
  return result;
}

B.

Is this function a thread procedure? Then you need to CoUnitialize before
returning.
If it's not a thread proc, you should not CoInitialize here.

Willy.