Replace normal " Build-in InnoDB" with "InnoDB Plugin" under DirectAdmin + CentOS 64 bits + MySQL 5.1
For some reason, under CentOS, Custombuild in DirectAdmin use "MySQL - Generic Linux (glibc 2.3) (x86, 64-bit) RPM file" instead of MySQL RPM files for Redhat. The different for these 2 packages are that, RPM for Redhat contain "ha_innodb_plugin.so" but not in Generic RPM package.
Compare files in Plugin folder on two different RPM.