Take the subject of your message enter it into ptc.com support search textbox and it'll be one of the first results on how to disable browser compatibility mode settings. This happens in IE 8 with Windchill 10 also. Try Firefox, Opera, or Chrome and you likely won't see message either.
We have had a number of challenges with our browser and PC settings in moving from Windchill 9.1 to Windchill 10.0. Here is a summary of our most critical browser / PC issues, and what we are doing about them.
Al Anderson
Issue 1: Message for slow response time that pops up asking if you want to continue. User receives this Message: ?A script on this page is causing Internet Explorer to run slowly? Action: To eliminate this message - Import the script below: