When you try to open the, uh, Open menu in different versions of Revit and AutoCAD, it just kind of sits there. It turns out, that a recent Dropbox update was causing the issue. Updating to the current Dropbox looks like it’s making everyone happy.
This was reported as a problem with Revit 2014, and we just had a client still using Revit 2013 that had the exact same issue. It looks like any recent version of AutoCAD is choking on it.
It’s a very strange issue when one seemingly disparate piece of software interferes with another, but we love the easy fixes around here!