bind stop respondig

[marcello1969]

Hello, I'm using bind-9.2.4-30.el4_7.2 on a CentOS release 4.7 (Final)
Randomly without any messages in log,named services stop responding, it's also impossible to restart it. when I try a "service named restart" it not respond and I have to kill it with a klll -9

Someone could give me a suggestion where to look or any work around ?

Thanks and sorry for my worst English.

Best Regards

Marcello