DSM-G600, DNS-3xx and NSA-220 Hack Forum

First of all, hi everyone

I just bought my DNS-323 last week, paired with a couple of Seagate Barracuda 400Gb and I'm extremely happy, I only have an issue with iTunes.
I set up the iTunes server, and with a couple XP machines on the network I have absolutely no problems accessing it: the only Mac (it's a new iMac, bought 15 days ago) has this weird behaviour:

I open iTunes, I see the NAS icon, click on it, iTunes loads the songs list, I click on one, the song starts... exactly 15 seconds later it stops and the NAS icon disappears from iTunes.

I close iTunes, open it again... see above.

Any ideas?!

Thanks!

Alex