I\'d like to reopen the question posed here and here about testing file uploading within Nightwatch.js which uses selenium.
Both links have the recommended solutio
I'm not sure why you're having these issues, maybe check to see if you are using the latest version of selenium server and nightwatch. This code works for me 100% in Chrome, Safari, Firefox, IE7/8/9/10/11 (not tested in IE6 but assume it as well).
driver.setValue('input#fileUpload', __dirname + '\\testfile.txt')