Windows Remote Desktop blackscreen issue

Remote desktop became a necessity in my daily work and it not only allows me working at home but also access a lot of information while on the road (e.g. for country specific resources).

Today when I really need to log in to my office PC, it showed a black screen AFTER logged in.  After some connect/disconnect/reconnect, I finally turned to Google.  Here's the solution:
Using Ctrl+Alt+Home to bring up the "lock screen" menu of the remote computer (in Win 7 that's lock screen, log off, task manager, etc.) Then choose "task manager".

Wow, the desktop is back. 

I'm not sure whether this is related to I locked the screen when left office.  Will give it a try tomorrow.

BTW, Ctrl+Alt+Del will bring up the local PC's lock screen menu.