Hi, René, sorry I missed your message.
Please have a look at this script.
iconoun.com/demo/classes/demo_UTF8_
...
It uses the $repair (second argument to the constructor) to tell the class to try to repair invalid UTF8 characters. I do not have any way to test on Windows, sorry. This script has highlight_file(__FILE__); so you can copy / paste the code.
My Twitter handle is @RayPaseur and my GMail is Ray.Paseur@
If you can post a link to the demo showing the error, I'll be glad to look into it, thanks.