We have previously developed a RuleBase in 10.1 which we have imported into 10.3 using the built in upgrade functionality. This RuleBase is designed to be a machine to machine interface and as such is entirely reliant on data fed inputs to make determinations, there are no question screens or interviews.
We then attempted to import some of the ".xds" files we had created in 10.1. There are over 160 of these, typically including over 120 data items in each with multiple entities and instances.
When we import these into 10.3 we get an error message which reads:
+"System.NullReferenceException: Object reference not set to an instance of an object.+
the simple solution is for us to re-input the ".xds" files in the debugger, but given that it took it over 2 weeks for our team to input the ".xds" in the first place, we obviously would like to explore other options first!!
I've got this working on the copy of the rulebase I had, it's because your entity / relationship public names don't match the .xds file, possibly as a result of the upgrade. I've sent you an email about this.