CMS Validation Error*

My client gets a validation error every time they try and create a new CMS item, even though all the fields are correctly filled out. The error shows after they hit the Create button. And then, when they edit the CMS item, the Create button becomes inactive and they do not have the option to Save as Draft. I know they have not exceeded their max limit for CMS items. Would anyone know what would cause this?

Thank you in advance!

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