Recently I bought an iPod touch 2nd generation.
When I connected it to my 17″ iMac PPC which had USB 1.x ports, it complaint with Error -50. After googling I found a clue that it would be related to USB 1.x. So, I connected it to my MacBook with USB 2.0 ports. This time it was successful to sync. After doing so, I tried connecting it to my PPC iMac again. And do you know what? It could be synchronized without any problem!!!!
So, it made me think that Apple somehow blocked its synchronization with old Macs with USB 1.x but once it is done, there is no restriction like that. So, it is like shallow prohibition of sync.
So, if you also suffer this problem with your iPod touch 2nd gen., try connecting it to other Mac with USB 2.x first and retry it with your Mac with USB 1.x.