I ran into the same problem. I work with a MacBook Air. What worked for me was the combination fn-control-alt/option-delete. Hope this helps any of you!
Some of our clients use the MAC connector to connect to our vWorkspace VDI environment. We have setup a screensaver that locks the screen after some minutes. On a windows PC, the user can press CTRL-ALT-END to unlock the screen. However, on MAC's without the END button, users can't get out of this unlock screen.  We have tried different combinations, but nothing seems to work.  Any idea's? 
How to unlock (cltr-alt-end) on Apple MAC