Xperia 10 mini sync problem

[RamboFreAc]

So... First of all.. My xperia 10 mini wont sync while using wifi, spotify goes offline then.
I've reinstalled my phone completley, still doesnt work.
however, i can sync while using 3G, but not all songs..
I thought i had full memory ALREADY! but no.. that's not it. I tried to sync another playlist, and remember, i already had one playlist synced. (but not all songs ofc, that's the problem)
And even there, it syncs a few songs, but not everyone. 
What sh*t is causing this?!