Hi Joe,
Did you only set the conditional branch that turned out to be True, but did not set the conditional branch that turned out to be False?
Like this:

I would recommend you create two business rules, each contains an action.
For example, at the beginning you only have one business rule, and its action is If True, then set Business Requirement, and Shows an Error Message.
So you can create two business rules, one action is If True, then set Business Requirement. The other action is If True, then Shows an Error Message.
Don't forget to deactivate the original business rule.