[CentOS] Xen crashes?

Is anyone else having problem with Xen Crashes or can provide hints why this
happens?
I can resolve it by restarting /etc/init.d/xendomains but I'm curios why it
happens, the machine
is running 64bit Centos 5, 16GB memory. I have some other programs reporting
exhausted
shared memory so maybe thats a cause?

kernel: xenbr0: port 4(tap1) entering disabled state

Greets,
Chris
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