This may not be related to the figure/information you are actually entering at the time. Some of the fields in the Contract area are Workforce Census required- so are mandatory. If one of the fields is not populated, you will be unable to save the contract. This is so that things aren't missed throughout the year to save you time during the Workforce Census. If you look behind the message that pops up, you will see the field causing the error showing in red. Populate this field as well to save the contract.