I think once you extended in July, any other subsequent vacation adjustments are tied to the extension CH limit (days*6 + 6) for that vacation week.

I would believe the error msg and submit the max slide that doesn't give you an error. Call them Mon 8am and talk to them. If it really is a glitch I'm sure they'll work with you to fix it.

Does the vacation buffer help you get rid of some of the c/o R days?