User is trying to create expense entries for different employees from the same expense item, but the Reimbursable flag is sometimes checked or unchecked for that expense, depending on the employee selected.
This can happen if the project has a fee schedule and you have checked the Reimbursable flag for the expense item against some employees while un-checking it for others in the fee schedule. When creating the expense entries, BQE CORE brings forward the Reimbursable flag from the fee schedule along with the special rates you have set for each employee. Check CORE Help Center for details on fee schedules.