This may not be the same for everyone but I recently had this error at work and it was doing my head in.
When a user got upgraded to IE11 from IE8 and went to a #SharePoint site, they were presented with a nice #ActiveX error that just wouldn’t go away! After lots of Investigations and Googling I still couldn’t find a solution.
Now we don’t get any #ActiveX issues within the sites we added to the trusted site lists.
As I said above, it might not apply to everyone but it certainly worked for the company that I work at.