The version of the JDK that you are using is too old. The Mendix Runtime requires at least update 22 of JDK 1.6. Note that JDK 1.7 is not yet supported because it is not stable yet.
The Mendix installer installs a recent version of the JDK if there is none. However, it does not upgrade an old JDK installation and I've submitted a ticket to get this fixed.
See also https://world.mendix.com/display/refguide3/System+Requirements
Also take care that any server you deploy Mendix on runs a recent JDK 1.6.