I upgraded from RoboHelp 9 to RoboHelp 2015 this spring.
My company's products are SaaS cloud-based applications. I generate Web Help output for a product. I deliver the output to our Product Development team, who then commits the content and all RH output files to their SVN source control project. The help system is then deployed together with the application as a WAR file to a web application server. Context-sensitive mappings are maintained in a properties file.
After a deployment to our pre-production server environment, it was found in QA that my web help content would not open using Internet Explorer 10. It threw the following message: "Object doesn't support property or method 'registerListener2' " and it references the whproxy.js file.
The help file opens fine in Internet Explorer 11, Mozilla Firefox, and Google Chrome.
I downloaded and installed the 126.96.36.1998 patch for RH 2015. It did not resolve the problem.
Does the same occur if you view the help before passing it on? If it does then check the developers loading all the files. Whilst I believe this may have been reported before, it was only one or maybe a couple of occasions.