Assuming that the fix is to simply add a space, it would seem a fairly simple process to use the RoboHelp Multi-File Find and Replace tool to search for </html> and replace with a space before </html>. This should update all topics and cause the change to be sensed.
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I have had similar problems with files disappearing (images in may case) and I also found that a "null edit" forcing robohelp to re-save the topic helped.
An easy way is to select all topics in the Topic list, give Edit > Properties, and make a meaningless change (I changed an item in the ToDo list which I do not use). Then give File > Save All. This forces RoboHelp to open all topics and should get your missing topics back.
Thank you both for your assistance.
I've tried both suggestions, but for some reason neither solution worked.
However, what I found was that I needed to click on Tools>Update DHTML Effects in Topics.
Being relatively new to this, I thought that when converting from 7 to 8 that this would have been done automatically, however it appears that when converting the project, this doesn't happen automatically.
Having said that, I'm very happy that I don't have to go through the huge number of topics in this project in order to correct that issue...
Thanks again for your help,