Hi Nick,
First off, I would caution you from creating such a big "kitchen sink" form. You should consider breaking it up into separate forms that communicate with each other. That will reduce load time and make it easier to maintain down the road.
To answer your question, two things I can think of...
- typically, the rule will change to "The expresion..." when the data source changes. For example, you delete the field or rename it. Rename should result in the rule automatically updating the rule condition to the new field name but if your form has too many rules and an error in one of them, the rule parser may stop with the update.
- check for rule errors - go to Rule Inspector and scroll through looking for red text. If there is an error, please fix it. The rule parser may fail because of these. You can also export your form as source files (file->publish->export as source files) and open up the manifest.xsf and scroll through the RuleSets section. Sometimes, updating this to be correct (and then saving, and right clicking the manifest.xsf to reopen in the Designer) is the fail-safe approach, but be careful - it is a sharp knife and you should make backups.
Good luck with all of the dishes piled high in the kitchen sink....
:)