Why is "stderr" not constant in the second scenario??

I'm new to Visual Studio 6.0 and am having difficulty understanding the differences between the standard Microsoft C Libraries used when compiling a simple console application. Here's my C code example:

#include <stdio.h>

static FILE *_logFile = stderr; /* Line with error */

int main(int argc, char **argv)
{
 fprintf(_logFile, "hello World");
}

There are two scenarios:
1. In the "Project Settings" Dialog under the "C/C++" Tab I set the "Category" to "Code Generation" and then the "Run-Time Library" to "Single Threaded *" or "Multithreaded". The Code compiles without warnings or errors. When I run the exe "Hello World" is printed (as expected) to the console.

2. I set the "Run-Time Library" to "Multitheaded dll". When Attempting to compile the code I get the following error:
error C2099: initializer is not a constant
It refers to the line I've marked.

So here's my question: Why is "stderr" not constant in the second scenario