From http://alanmiller.awardspace.com/context2.htm:
Context Menus
There is a keyboard shortcut to open a context menu. Ctrl + Shift + F10 works in many programs, unless the application uses that key combination for something else. There may actually be a dedicated key on your keyboard to open the context menu, usually more universal and reliable, looking something like the key on the right in Figure 2.
So actually, you need to send:
Send('^+{F10}')
Christof