I had an issue where a user was trying to modify some webpart settings on an OOB sharepoint teamsite. But everytime the user would mouse over the dropdown on the webpart to display the options to modify, the dropdown would not appear. Even more odd was it would work just fine on the 3 webparts on the page.
The error message I was getting was a Error: ‘style.display’ is null or not an object (type) error. My first thought was how did this person add some custom code into this site, and then i remembered you can absolutely do that with a Content Editor Web Part (CEWP). The webpart that was having the problem was not a CEWP, but there was another that happened to be working, but was a CEWP. I checked the source view on the webpart (SharePoint 2007) and sure enough there was a funky DIV tag in the source.
<DIV id=WebPartWPQ5 WebPartID=”RandomGUID” HasPers=”false” width=”100%” allowDelete=”false”>