There is a problem that Apple needs to fix (ha ha.. there are many but I digress) with ATH hanging after an ios device has been removed from the USB slot.
Re-inserting the device creates a new ATH instance which has some kind of conflict with the existing (hung) instance.
The solution is to end the process using CTRL-Alt-DEL and under processes there will mostlikely be two (or more). Kill them both, re-insert your device and it should sync OK.
Apple - please fix this (and the firewall problem) immediately.