The first thing you should do is ensure that CrazyTalk is updated to the latest version which is 6.21. If you need it, you can get this update from within your Account.
Then also make sure that your graphics drivers are updated to the latest available. You can get these from your computer manufacturer or from Nvida, ATI etc.
If you are using Intel Graphics with Windows 7 then there is a special fix for this problem. To find out more, please refer to the link below.
Hope this helps.