[CentOS] Fedora 9 domU on CentOS 5.2 dom0 - very unstable?

I am running a Fedora 9 domU on CentOS 5.2 dom0, and it is quite 
unreliable. Every few days I have the following phenomenon:

- many applications do not work at all (e. g. Nagios 3.05 stops checking, 
but the cgis work perfectly, the web server works as well)
- system processes run into time outs (e. g. logging in via ssh runs into 
timeouts <<"connection reset by peer">> after many seconds, logging into 
the console does not get finished ever, no error, no refusal) and similiar

All I can do then is destroy the domain (xm shutdown does not lead to 
anything either).

Is this a known phenomenon? Is there any way to work around it? I do not 
have these problems with CentOS 5.2 domUs on the same machine (at least not 
that massive).

Every hint or help is appreciated.

Dirk