Unable to check-in file – required field is blank
Problem:
You try to check in a file in a SharePoint document library and you are asked to ensure all mandatory fields are not blank. However, all the fields on the form have been completed.
Cause:
This problem is most likely caused by required columns that have been set to hidden in the content types.
Solution:
Check the content types in the library for hidden columns. Reset the columns back to ‘Optional’ and then ‘Hidden’ again.