It does not seem to make any difference what file, I was using the grep-changelog file in the bin folder for testing, but any text or source file seems to cause the problem. I was visiting the file by dragging and dropping it into the emacs window. Visiting a file using the menu or 'C-x C-f' does not cause the problem. Starting emacs with emacs -Q crashes if a file is visited. I have attached a traceback from the zlib-available-p function. I couldn't paste it here because it contains null characters (^@).

Regards
Bill Farmer

On 26/11/2014 15:55, Eli Zaretskii wrote:

Date: Wed, 26 Nov 2014 11:34:52 +0000
From: Bill Farmer <williamjfarmer@yahoo.co.uk>
CC: dmoncayo@gmail.com, 19181@debbugs.gnu.org

I have downloaded a built version of zlib1.dll from the zlib web site
(http://zlib.net) and copied the file into the bin folder of the emacs 24.4
distribution. This fixes the problem, as this version of zlib does not have a
dependency on libgcc_s_dw2-1.dll.

Great, so your problem is solved.  I've now mentioned zlib1.dll in
etc/PROBLEMS as the potential source of such crashes.

However, I'd still like to understand why Emacs loads zlib1.dll when
you visit a file.  Could you please help me figure that out?

First, does that happen with any file, or just with a few particular
ones, and if the latter, then which files trigger that?

Second, how do you visit that file, exactly?  "C-x C-f", via the menu
bar, something else?

And finally, does Emacs load zlib1.dll if you invoke it as "emacs -Q"?
If "emacs -Q" doesn't load zlib1.dll, can you try finding the
customization in your ~/.emacs that causes this?

There are only 2 functions in core Emacs that might load zlib:
zlib-available-p and zlib-decompress-region.  So another way of
finding out why zlib is being loaded is to "M-x debug-on-entry" both
these functions, and when Emacs pops up the Lisp backtrace, see who
called them.

Thanks.