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Sounds like you have some corruption in the OS.
What I advise, is for you to shut down the mac.
Start it using command R, and do a recovery install.. ( do not do an erase and install, just a recovery install)
This will reinstall lion, without wiping out your programs and files.. Basically, its a repair install.
Heres further info on how to do it..
The recovery install, will resolve the issue your facing.. ( im surprised the Apple people didnt attempt it )
if you get stuck, or run into any issues, let me know!
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