In your Setup > Rules > Individual Handicaps, you have the Maximum Handicap Game Score and Maximum Handicap series score set to zero.
These are new rules that are set, by default to 9999 for series and 999 for game.
The purpose of these new rules is for use with the new USBC rule that allows leagues to limit the handicap game and series scores. So if your league voted to cap the limit of the handicap 300 score to be 300, then a 300 would be entered. If your league voted to cap the limit of the handicap 900 series score to be 900, then 900 would be entered.