This can occur when a customer list is imported into Control where required data fields are missing. For example, Default Tax Class, Contact Last Name, Primary Phone Number, and Payment Terms are all required fields when creating a new company. The system will not permit you to save a new company with any of those fields blank. However, importing customers into Control will create the company and save the record with the missing fields.
Days, weeks, months or years can pass before a specific company will be accessed. When an order is created for a company that has missing required data, the result will be an access violation when trying to save.
Now return to the order or estimate and you will be able to save it.