I haven't seen this error posted before, so I'm posting it.
When "Enable lockCode encryption" is turned on the lock device page, I'm unable to add a new user and code using Lock Code Manager. Here's the error thrown by each of my locks:
Turning off lockCode encryption allowed the new user & code to be added right away to both locks.
Just in case this is specific to particular locks here are the details:
Both locks use the Yale zigbee lock driver.
Tagging @mike.maxwell