Unfortunately, your post didn't mention that.. Next, if you've already uninstalled it, first, make sure that RealPlayer has been removed from the Task Scheduler section. It tends to try to run from the Task Scheduler even when uninstalled. (Open the Control Panel, then "Administrative Tools", then "Task Scheduler". Remove all RealPlayer when found.
Next, follow all the steps in the links below to find any remnants in the registry.
In the second link, you'll also note there are 3rd party context editors which are available for free.
Hoped this helps.
I've tried ShellExView, CCleaner, Glary Utilities and editing the Registry, but have not been able to remove RealPlayer from Context Menu [nor M.S.E., DOS Prompt or Library]. Is there some other way ?