Latest update of the openssl package from CentOS breaks Parallels Panel 9.x. Errors are displayed in the /var/log/sw-cp-server/error_log file when Panel is trying to start.
The problem has been fixed since version 9.5.0.
Download the appropriate package using the wget utility. Example for CentOS 5 x86:
#wget -c http://kb.parallels.com/Attachments/12669/Attachments/sw-cp-server-1.0-6.201004011105.centos5.i386.rpm
Install the downloaded package. Example for CentOS 5 x86:
#rpm -Uhv sw-cp-server-1.0-6.201004011105.centos5.i386.rpm
Reference : http://kb.parallels.com/