As has been previously reported in such places as:
https://sourceforge.net/mailarchive/forum.php?thread_name=AANLkTinZvxgC9ezp2P3UCX_a7TAUYuVsp2U40MQUV6qr%40mail.gmail.com&forum_name=gnumex-users
https://sourceforge.net/mailarchive/forum.php?thread_name=AANLkTin8%2B8AL%3DjSremgjXLs4bzRazktX6GOr9y02Pk4s%40mail.gmail.com&forum_name=gnumex-users
https://sourceforge.net/projects/gnumex/forums/forum/322756/topic/4011182
https://sourceforge.net/tracker/index.php?func=detail&aid=2962883&group_id=93315&atid=603906
Gnumex does not currently work well out of the box with 64-bit versions of Matlab. If this project is currently being maintained, I hope someone can review the attached patch which I believe fixes these reported bugs and allows Gnumex to work properly in both Win32 and Win64 Matlab. An addition I have made that has not been reported in quite the same form yet is to use the selection for the environment/linking type to determine which version of nm.exe to use for making the lib/def files. When both Cygwin and MinGW are installed in default locations, Gnumex currently uses Cygwin's nm.exe, but this will not be able to read the 64-bit lib files from matlabroot\extern\lib\win64\microsoft. There are workarounds of course, but the behavior in the patch of looking where the user has selected makes more sense to me.
Patch file to fix bugs with 64-bit Matlab