When filling out an InfoPath form, you might see an error message saying "Some rules not applied." There may or may not be more information about the specific error. This error is generic and can occur under a wide variety of circumstances.
If you are filling out a form and see this error, and you are concerned about losing the values you have already filled in, your best bet is to first save the form values locally. Then, contact an administrator who can help you troubleshoot.
If you are designing a form and see this message while testing, you should troubleshoot the problem and fix it before providing the form to others for filling out. If the error occurs sometimes but not always, and the form needs to be available despite the possibility of errors, you should consider adding an OnFailure message to the field that generates the error. An OnFailure message can be as specific as you want, and can help form fillers more effectively than the generic error message.
More help with validation rules
Here are some links to help smooth the experience.