The validation error Horse has no Agistment Charges can occur when a horse arrival procedure is recorded AFTER agistment charges have been processed.
To resolve this you will need to review and alter procedures recorded against the horse so they are chronologically correct. To review what has been recorded, open the horse record;
Search for the horse in question
Examine Transactions to review costs for the month, and Procedures to check Arrival/Departure dates and amend as required.
It is important to address Month End validation errors and then click Re-run these Checks to ensure your Month End process completes smoothly and your accounts are up to date and accurate.