asterisk users - Jan 2011 - Polycom SoundPoint IP 650 freezes on boot after adding just one custom ringtone

Hi I'm new to this list, so please forgive me off-topic or RTFM-questions.

I have an asterisk/elastix driven phone-environment using Polycom
SoundPoint IP 650 as extensions. When adding just one custom ringtone
(~57KB) in a proper format (ML.wav: RIFF (little-endian) data, WAVE
audio, ITU G.711 mu-law, mono 8000 Hz) the phone boots well. But after I
have chosen the custom ringtone as my ringtone the phone works without
problems until next reboot. I have to rename my custom ringtone for that
it is not found on boottime, change the ringtone to a default one and
reboot the phone to make it work again.

My questions:
1. Where are configurations done with the Webserver of the phone stored?
I guess must be somewhere in the tftpboot-dir on my asterisk/elastix
server. But I can't recognize any file changes (compared timestamps)
2. Where can I find out how many space is left on my phone (some
PDF-Guides from polycom say that about 160KB of custom ringtones or
about 120 items in contact directory are fine for the phone - I have 7
items in my contact directory and just one (57KB also tried 38KB) custom
ringtone
3. What else could be the problem for this behaviour?

Thank your for helping me gettng started with asterisk

Marco