This sounds like a problem between dotnetnuke and the windows browser. Have you tried using the regular browser and see if the webpage works without it?
If I remember correctly isn't DotNetNuke a CMS system?
Its all I can think of. I'm not certain which browser powers FileMakers webviewer in Windows 10. Its probably edge, but I can't say for certain.
I get the message when I open the page in internet explorer, but NOT when I open it in the Edge browser. FileMaker uses IE on windows, I am not aware that this can be changed.
Customer1: I cleared the cache and the page now works in IE and FileMaker
Customer2: I cleared the cache and the page worked in IE but still shows the error in FileMaker
It can't. The webviewer is not a full-fledged browser either so some things just don't work.
This page has always worked. The error page just started for a couple customers. I was able to fix one by clearing the cache. The other this resolved it in IE but not in FileMaker