Hi, I had the same problem [closed iCal date stuck at 17 July] and tried the answers above, which didn't help at all. This answer found at
http://forums.macrumors.com/showthread.php?t=395610 did the trick.
First, All applications (except Finder) must be closed.
On the Finder menu bar, click on "Go," then on "Home."
Go into the Library folder
Delete the Caches folder > *I only deleted the com.apple.iCal folder*
Go into the Library / Preferences folder
Delete the files: com.apple.iApps.plist; com.apple.iCal.helper.plist; and com.apple.iCal.plist
Restart system