Thanks for the advise.
I did not know that php was case sensitive...
Here is the physical path in the browsers detailed error information.
Physical Path C:\inetpub\wwwroot\mainFrame1.html
I've un-installed and deleted the whole IIS install including using safe mode F8.
After and before I ran a case and root folders reconfigs and the same http error arrives.
The site was prioly made and ran before on IIS.
How do I get the frames to follow the index.html as DW F12 runs the home page but not the frames via btns, anyone?