I have this problem, but cannot reset sync services. There is no iSync menubar icon, iSync refuses to launch, and trying the Terminal method generates an error loop:
2014-02-16 20:49:37.059 perl5.10.0[88673:d07] [26b730] |Mingler|Error| failed to connect to the server: NSInvalidReceivePortException connection went invalid while waiting for a reply
over and over, about every 10 seconds, for as long as I'll let it run (I've gave it around half an hour at one point).
There are very strong warnings not to mess with anything in the SyncServices folder. As near as I can tell, syncing of contacts and calendar items to my phone is actually still working just fine--but I can't backup or sync my iPhone, manage what apps or content are synced to the phone, etc.
OS X 10.6.8, all updates. iTunes 11.1.4(62)
Solved: Deleting ~/Library/Application Support/SyncServices/Local solved the problem. Found in this thread: https://discussions.apple.com/message/10070454#10070454