QuickBooks error code C=3 Accounting and finance tasks have been made easy by the QuickBooks software. It offers a wide range of services, for instance generation of invoices, payroll services, writing checks and much more. QuickBooks is an amazing tool for your business. However, at times working on QuickBooks is affected by some errors. These errors can be very annoying, therefore it is recommended that you fix these errors as soon as possible. Error code C=3 is one such error. Error code C=3 happens only on Mac. Occurrence of the error does not allow you to open a Quickbooks file.