Boot Camp / Partitioning Weirdness
Thanks for the update, your partition table looks fine.

One more thing to try would be to boot from the recovery system or installation media, or access the drive from another Mac via Target Disk mode and try to resize the partition from a Disk Utility instance that isn't booted off the partition you're trying to resize. Unfortunately, it's fairly unlikely this will help - I've seen more instances where it didn't than where it did.

If Disk Utility can't help you, the only solutions are:


Back up, erase and restore
Try your luck with something else. In the past, resizing via parted (an open source Linux utility) has worked for me in such cases. I'm writing this on a MacBook Air with an OSX installation that survived the procedure unharmed. There's a bootable Live CD/DVD distribution of this available, called "Parted Magic"; "GParted Live" is another, which seems to be a bit more user friendly. You can burn either to disc and boot into it by holding the option key during the boot chime, as usual. Then shrink your main partition - this will take a while, as it needs to move the data to free up the space at the end of the partition. There is of course a certain risk associated with this, so make sure you've backed up and are prepared to go through with option 1 instead. Make sure to unplug your backup disk during any such procedure. One issue with using another tool is that unlike Disk Utility or Boot Camp, this won't move the Recovery HD. So your best bet is usually to shrink by the required amount, then grow it again to the original size. Doing this will then "unstick" Boot Camp/Disk Utility, and they'll be able to proceed with the shrinking as normal.