I had this exact same proglem. I recieved this error both when I opened up any page in the browser and when I opened up the Handler Mappings in IIS. Like the original poster, I'm running IIS 7.5 with a recent install of Coldfusion 10.
I was able to fix my issue by doing the following...
1. Open up the ColdFusion 10 Web Configuration tool.
2. Remove all sites.
3. Add new site. Keep the default settings and save.
This is what fixed the issue for me.
Good luck!