Several things come to mind:
I kid you not, reverse what you have written as your condition, change cannot be blank, to blank. I can often get them the wrong way round, even though in my mind it makes perfect sense, what my condition is.
Why not validate the fields before you need to submit the data? That way you should see an asterisk or red dash around your fields before some information is input into the fields.
If the validation is based on several conditions, check each condition separately, step by step..
Add a dummy text field to the form and set it's default value to the field you are validating against. Then you should see what Infopath sees and the field value and why it's not validating as expecting.