I'm no longer able to lock my screen with Ctrl-Alt-L, and

$xscreensaver-command -lock xscreensaver-command: already locked.  What is going on here? Is this functionality broken? xscreensaver-command -activate still works, but that doesn't prompt for the password when dismissing. $ uname -a
Linux hostname 3.0.0-17-generic #30-Ubuntu SMP Thu Mar 8 20:45:39 UTC 2012 x86_64 x86_64 x86_64 GNU/Linux

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Congrats on getting it solved, can you add that as an answer? :) –  fossfreedom Apr 10 '12 at 18:56
I wouldn't call it a solution as much as a clobbering of the running processes to get where I wanted. But I'll post it until and unless someone has an explanation of how this could have happened. –  l0b0 Apr 11 '12 at 7:27
+1 great - dont forget to tick the accept button. thanks. –  fossfreedom Apr 11 '12 at 8:14
If anybody knows how gnome-screensaver could usurp the place of xscreensaver I'll accept that answer. –  l0b0 Apr 11 '12 at 8:18

While investigating for a bug report, I found that gnome-screensaver for some unknown reason was running. The following workaround did the trick:
gnome-screensaver-command --exit && xscreensaver &

I'd like to emphasize that it's just a workaround, not an answer to why xscreensaver died nor how gnome-screensaver came to run.