Usually when Denticon hears of this happening, a 'Flash Alert' was created with 'Block Charges' selected.
When 'Block Charges' is selected, it prohibits the user from making additional charges to the ledger or edits within an existing appointment.
To resolve, you may edit the Alert to uncheck "Block Charges' or disable the flash alert.
Flash Alerts may be managed or viewed from the Patient Record by going to Patient / Flash Alerts.