From the GUI, clicking the 'Test' button in the JMX extraction program settings screen resulted in an error of "Cannot find ITLJMXJSR160Client". Running the TEST_JMX.BAT (which is in the Sentra directory) revealed that ITLJMXJSR160Client could be found, but it was incompatible with the default java version which was installed on the Sentra server. JMX requires JRE 1.5 or later. The default Java installation was JRE 1.4. The solution is to edit the .itl file and modify the JVM_LOCATION setting so that it references a JRE 1.5 JVM.DLL
[JMX_TEST]
JVM_LOCATION=JVM.DLL -- change this value, e.g. to C:\Program Files\Java\jre1.5.0_09\bin\client\JVM.DLL

In addition, there is an extraction program setting for the JVM location. This will also need to be modified, e.g.

Section Name=JAVA_SETTINGS
Key Name=JVM_DLL_PATH
Value=C:\Program Files\Java\jre1.5.0_09\bin\client\JVM.DLL

From Sentra V6.0 onwards, the extraction program JVM_DLL_PATH setting will be prompted for as part of the agent deployment wizard.