Thanks Everett and k. You both may now take the day off
That info file is a info.txt file needed by Alexa and others to display site owner details, said to add a nano point in page ranking but generally just good practice to use. However, it did seem to confuse the CMS because when I removed it the links from the info.htm file worked fine.
Pity to have to remove the info.txt file but some of those children pages have good rankings in search engines and I’d rather keep their URLs unchanged.
Enjoy your day off.