This would indicate the base pay is entered in a format not expected by the DfE. To check this please go to Admin > Personnel > Staff - find the member of staff and click onto the black cog next to contract and amend the base pay and update.
A contract with 0.00 as Base Pay will also generate this error, as a positive value needs to be entered (e.g. 11868.72)
Please check all contracts in scope for the Workforce Census, as there may be a missing base pay figure on an expired contact.
For further guidance on base pay please see p55 of the DfE Documentation: