Help with ERROR

Can anyone explain this ERROR I'm getting and if its a problem. Thanks in advance

Please provide screenshot of the rule. Can't tell anything from error alone. And what build you are on (should be the latest,

Was on .121 when ERROR occurred. Upgraded since your message to .123 (maybe I shouldn't have :smile: ) I was attempting to write this rule, but it isn't working correctly so far, its looping. However the ERROR didn't come back after upgrading.