Did this appear after you were finished with getting assistance in the HJT forum here, or did you have the problem before and was it just not resolved?
First, open Internet Explorer, click "tools" and choose "Manage Add-Ons"
If there is anything in there relating to this popup or anything else you do not recognize as being valid, disable it.
Then I suggest you reopen your HJT session.
Repost a new copy of your HJT log in the HJT forum and explain the problem briefly. You may want to PM the HJT member who helped you to begin with but in any case, post a new log here:http://www.bleepingcomputer.com/forums/posthjtlog.html