Compiler error

Dear Sir,

I am using Domjudge to set up ACM Contest in my school, everything is OK.

I can submit Java, C, C++ very well.

I also install cgroup and using chroot.

But sometime, I received error like this when I submit any code, just somtimes this happened, and when I rejudge them, I received CORRECT response.

Error text:

Compiling failed with exitcode 255, compiler output: /domjudge/judgehost/bin/runguard: illegal user specified: 7806 Try `/domjudge/judgehost/bin/runguard --help' for more information.

Can you show me how to solve this problem?

And I also run domjudge without root accout, I run it with an account with root privillege!

Thanks. I'm looking forward for your help!

Best regard,

Linh