CF11 Cfwindow problem Script: http://sbs/CFIDE/scripts/ajax/ext/ext-all.js:18

I am having a problem with all my pages that include Cfwindow after upgrading to CF11. There is a long delay (15seconds) and then the message -

Unresponsive Script

A script on this page may be busy, or it may have stopped responding. You can stop the script now, open the script in the debugger, or let the script continue.

Script: http://sbs/CFIDE/scripts/ajax/ext/ext-all.js:18

This happens also on the test page from CF11 documents cfwindow - ColdFusion, English documentation - Adobe Learning Resources

Apart from the delay, the page loads and works fine.

Is this a problem with with my installation following upgrade or a more general issue?

Regards

Richard