I have used the following free context menu graphic filetype converters:
Format Factory, Sagethumbs, XNView and NCH Pixilion. Each of them has caused Nexus Ultimate to crash upon clicking on it`s context menu.
20-10-2013 ADDITIONAL INFO:
I was still getting intermittant RMB context menu Nexus crashes so thought there may be another source of the problem. I have the DVDVideoSoft free program installed and thought it may have links to various parts of the system so I uninstalled it. During this operation it also closed down Nexus Ultimate but after the uninstall I called Nexus back by the shortcut. The result is no more crashes. Regarding selecting NEVER in the open sub-menus on mouseover section it keeps reverting back to ALWAYS.