Download Shellview: ShellExView - Shell Extension Manager For Windows
It will scan the registry for all the shell extensions. Once the scan is over and the list is displayed, you need to spot the context menu handlers. Sort the results using "Type", so that the context menu handlers are displayed together.
General rule here is to disable non-Microsoft context menu handlers *one-by-one* and verify if the problem is solved. If disabling one does not solve the problem, undo the disabled item and disable the next non-Microsoft handler. Do the same until the problem is solved and finally identify the culprit. Scroll right to see the Company Name column in ShellExView.
You can disable them ...they say "one at a time" and see what effect it has on the problem. You can do it a lot quicker by bisecting the list, disabling half of the entries in one fell swoop, rebooting and trying the right click. You just have to narrow it down. Then keep bisecting the list until it is just a few and do these one at a time. The problem is that you have to reboot between tries to get accurate testing of the results of your disabling.
The latest version of ShellExView marks all the non-Microsoft extensions in Pink for easy identification. All other types of shell extensions that ShellExView utility cannot recognize are categorized as "System" type.