LAN crashes after some time

[moxmox]

Hi everyone,
I'm running a pi in headless mode.
My power supply is a converted wall charger, rated 5 A at 5v. It powers the pi and a usb-hub. There is a 2.5" external hard drive connected to the usb-hub, my stereo connected to the line-out and an ethernet cable connected to my router. When I attach the power supply, the pi will boot up and after about 10s I can ssh to it.
Then I mount the external hard drive and use truecrypt to mount an encrypted file with music and start mpd and play some music.
So far, everything seems fine, but then, after some time, the pi will not respond anymore, the ssh terminal just freezeses, and my router will not show the pi with the connected devices anymore. I have tried attaching the pi directly to my computer. While the pi is connected to either the router or my pc, all leds light up, when I disconnect the ethernet cable, the ethernet leds will turn of, but turn back on, when I reconnect the cable. However, the pi is unreachable from the pc as well (when the pi is running normally, I can connect it to my pc directly and it works).
I did not change anything from the standard install, except:
- installed zsh, mpd, vim and my config for those
- compiled truecrypt

The time until the pi 'crashes' seems to be random, sometimes it is mere minutes, sometimes it runs for days.
Is this behaviour observable with other pi s, too, or is there a workaround?

sincerely,
mox

p.s.> I did google my problem, but I could not find anything relevant, except this (viewtopic.php?f=31&t=4539), but since I do not use deluge, this didn´t help me very much.