The cell or chart that you are trying to change is protected and therefore read-only
You may receive this error message if the current sheet is protected by password.
To unprotected go to Review Tab / Changes group. After that you must insert the password.
Error class: Office; the cell or chart that you are trying to change is protected and therefore read-only
Error type: the cell or chart that you are trying to change is protected and therefore read-only
Error message: the cell or chart that you are trying to change is protected and therefore read-only