This is from the users guide:
Unknown Servo Error
Run the Loader – Health Check test from the Remote Management Unit <ADMIN NOTE: Broken link has been removed from this post by Dell> or from the front panel.
If the previous step fails, contact support.dell.com
You can find the doc's online at: http://www.support.dell.com/support/edocs/stor%2Dsys/124t/
Hope this helps.