Hi Lisa and Margaret
Thank you for your replies. I recall seeing a thread about this issue a while back but could not find it whilst searching the forum last week (the search is awful, always ignores most of the words)

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Lisa, I have enquired with my developers and there is a call for a window called "main". However, this has apparently been the case for a long time for all our software products and no error message of the type of the one shown in my first post has been thrown so I am a bit puzzled.
Margaret, we have never changed the skins name. Also, I do not quite understand your solution. It looks like the call to the ehlpdhtm.js script is only present in the files in the Output folder so once I have done a find/replace exercise across the project, how do I re-compile these files (do I NOT clean the output folder?)?
Thanks again for your input.