In the last day I have started having a lot of brokenness on my Mac (MacBook Air running Mac OS X 10.6.2 with all software updates).

Most noticably, iTunes no longer syncs with my iPhone. It fails with a crash dialog reporting "AppleMobileDeviceHelper quit unexpectedly" and an error dialog "iTunes was unable to load dataclass information from SyncServices. Reconnect or try again later."

I've attempted the fix at support.apple.com/kb/HT1747 but it failed.

I've also been having problems (at first seemingly unrelated) with the horrible Cisco VPN client, which started giving me this error:

Error 51: Unable to communicate with the VPN subsystem

I followed the steps at www.anders.com/cms/192/CiscoVPN/Error.51:.Unable.to.communicate.with.the.VPN.subsystem which don't seem to work for me, although I can connect if I use the command line with sudo :

sudo vpnclient connect MyProfile

I had a look in the Console app at the diagnostic messages and I noticed a pattern, that a number of apps were reporting "BUG IN CLIENT OF LIBDISPATCH". The affected programs are:

• AppleMobileBackup
• AppleMobileDeviceHelper
• Safari Webpage Preview Fetcher
• cvpnd (the Cisco VPN daemon)

Of these, only the last is non-Apple software!

The common text in the diagnostic messages is:

Exception Type:  EXC_BAD_INSTRUCTION (SIGILL)
Exception Codes: 0x0000000000000001, 0x0000000000000000
Crashed Thread:  1  Dispatch queue: com.apple.libdispatch-manager

Application Specific Information:
BUG IN CLIENT OF LIBDISPATCH: Do not close random Unix descriptors

I'm beginning to wonder if there's a permissions problem, or corruption of an important library, ...

I should note that I've rebooted several times and verified the disk permissions and the disk.

Any help would be great!