Share heap between DLL's

I have a quite large project written originally in BC5, and I am
currently porting it to Visual C++ (VS2005) using OWLNext
(www.owlnext.com).

The program itself is now "converted", and it is running, but with
errors.
The error that concerns me the most is that I get heap error when
trying this simple thing:

1) Creating a char*
2) Setting this char* to a new duplicate of another char* - this is
done in another DLL.
3) Deleting this char*

Example code:
void ParseLine(char* line)
{
   char* xNumStr;

   xNumStr = strnewdup(line);
   delete[] xNumStr;
}

strnewdup is a part of OWL (and owl-dll) and goes like this:
strnewdup(const char* s, size_t allocSize)
{
  if (!s)
    s = "";
  int alloc = max(strlen(s)+1, allocSize);
  return strcpy(new char[alloc], s);
}

It's the delete[] in ParseLine that gives the error, which states that
the heap is corrupt (I am running in debug-mode).
If I move the strcpy-call from owl-dll to within ParseLine code, I get
no error.

This code works in BC5, but not in VC. I suspect it has to do with the
heap being private for each DLL, but I'm not sure. If I need to change
the code, I have to do it hundredths of places, and I really do not
want to do that.

Can anyone tell me why this error occurs, and maybe help me with how
to fix it without changing the code too much?!?