Update - Replacing the X codes didn't change anything. Still getting the error. Now support is saying we have to correct all our missing marks and unexplained absences before we can Create & Validate the census. This has NEVER been the case in the past. You create and validate, it tells you that you have missing marks, you correct them. I can't even get that far. I have a very strong suspicion that, even after we correct missing marks and unexplained absences, we'll still see the same error (Your attendance codes are not DfE compliant).
I'm desperate for help!