That is one of the github sites. There's also https://github.com/bruceravel/demeter which is the program that makes use of ifeffit. The installation that is used comes from http://bruceravel.github.io/demeter/.

I copied the XP .dll because I wanted to see if the error would change indicating that it is actually calling the correct file (when it's there of course). The error does change:

Can't load 'C:/demeter/perl/site/lib/auto/Ifeffit/Ifeffit.dll' for module Ifeffit: load_file:%1 is not a valid Win32 application at C:/demeter/perl/lib/DynaLoader.pm line 190. at (eval 18) line 1.

as would be expected. The ifeffit / demeter software is not to blame because it's only our office that can't get it to work and it does strangely work on our computers in safe mode, but not clean boot mode.

I can try rebuilding the ifeffit library from the source code though if you think that may help.