To be effective, the namespace URI http://www.exoplatform.org/xml/ns/kernel_1_2.xsd must be target namespace of the XML configuration file.

<configuration xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 

               xsi:schemaLocation="http://www.exoplatform.org/xml/ns/kernel_1_2.xsd http://www.exoplatform.org/xml/ns/kernel_1_2.xsd"

               xmlns="http://www.exoplatform.org/xml/ns/kernel_1_2.xsd">

   ...

</configuration>