This message is generated if the languages selection of the current script contains a language which no longer exists in your database (ie. it was most likely deleted).
You will not be able to generate a diary until this message is addressed.
•Edit the List of Languages: Use this solution to select another language, instead of the one being referred to by the present message.
•Open the Tokens and Translations Manager: Use this solution to go into the tokens and translations manager and modify the options of the language being referred to by the present message.