Error 4380 arises when a staff member is given a fixed term contract, but no end date is provided. Click on the Error link to access the staff profile, then click on the cog next to the contract to open it up.
Check whether the contract is meant to be Fixed Term, and if so enter an End Date. If it is not fixed term, then amend the Contract Type. Click Update to save the contract information, then recalculate the Workforce Census.