Error when searching in webhelp help

We are using RoboHelp 2015 to generate webhelp.   Don't know how long this has been a problem, but was just reported after a service pack release of our software.  When the user is in the 'full help' screen and either clicks on the 'Search' button on the left or types something into the search field at the top and clicks 'Go', the following message is displayed:

That line in whutils.js is just a comment.  Any ideas?

Phil