I have a pretty decent list of the advantages of using a Rules Engine, as well as some reasons to use them, what I need is a list of the reasons why you should NOT use a Rules Engine
The best I have so far is this:
Rules engines are not really intended to handle workflow or process executions nor are workflow engines or process management tools designed to do rules.
Any other big reasons why you should not use them?
I will give 2 examples from personal experience where using a Rules Engine was a bad idea, maybe that will help:-
Lesson: They are called "Business Rules" for a reason, do not use rules when you cannot design a system that can be easily maintained/understood by Business users.
Lesson: Requirements tend to change a lot during initial release changes and do not warrant usage of rules. Use rules when your business changes often (not requirements). Eg:- A software that does your taxes will change every year as taxation laws change and usage of rules is an excellent idea. Release 1.0 of an web app will change often as users identify new requirements but will stabilize over time. Do not use rules as an alternative to code deploy.