Installation/upgrade by Autoinstaller stopped with the following error message:
Error: Unable to proceed with the installation until the package php-mcrypt-5.1.6-15.el5.centos.1.i386 is removed from the system. Not all packages were installed. Please resolve this issue and try installing the packages again.
RedHat have not provided mcrypt module for php53.
As a possible workaround, you should uninstall the package first:
# rpm -e php-mcrypt
Then you should install/upgrade Plesk by autoinstaller. After that you can use php53u-mcrypt - A module for PHP applications that use Mcrypt or build it by yourself.