Please reduce your code to a small, self-contained example that still exhibits the error. Most likely, this will mean you have to create your main file and the file that is loaded via require, but neither should be more than 10 lines long. Once you have these, we can look at them and try to reproduce your problem.

Are you sure that the perl.exe that you are explicitly invoking is the same perl.exe that your file association is set up for? Output $^X from within your Perl script to check.