XU = eXecution Unit so based on your explaination I would say that "JRules" is complaining because it cannot find your ruleset in your ruleapp and hence crashes.
Open the jar file (ruleapp) inside you should see at least one folder named: "your ruleapp name"
in it a folder named: "your ruleapp version" (possibly "1.0")
in it : "your ruleset name"
in it : "your ruleset version"
and in it your rule atrifacts.
Makes sense?
Possible ruleset path:
1/ ruleappName/ruleappVersion/rulesetName/rulesetVersion
2/ ruleappName/rulesetName/rulesetVersion
3/ ruleappName/ruleappVersion/rulesetName
4/ ruleappName/rulesetName
Note: Version is optional and if not specified then the latest version deployed will be used.
I coded a whole set oh Helpers and Factories for JRules (7.01 and 7.1) - some tweaks may be needed with version 6
Let me know if you are interested.
Basically there are RTSHelper and RESHelper libraries
containing static methods to create queries, business rules, extractor, ruleset, ruleapp, deploy, create a ruleset based on query and so on...
Remove ruleapp from RES after execution and a lot more...