Unable to load the parallels driver error

Hello,
Recently, I am having issues on Parallels 4.0 with CentOS 5.4. It won't start on Virtual Machine.
When I try to restart the computer and the physical server to resolve this problem the same error occurred.
How can I fix this without having any issue?
I need your suggestion as soon as possible.
Thanks for any kind of help.
CentOS 5.4 – Parallels Management Console
Unable to load the Parallels driver.
Restart the physical server and try again.
