QuickBooks error 6123 is a company file error that gets triggered while opening, upgrading, or restoring a company file. The error can get triggered due to various reasons, such as the corrupted QuickBooks program or damaged company file. Once you know the exact cause of the error, finding the solution becomes easy. This linked article has explained the causes and the solutions to the error in simple words. Read the linked article to know the fastest way to troubleshoot the error. If you have any doubts related to the error or the linked article, dial 800-583-0572 and get answers to all your QuickBooks-related questions from a QuickBooks Expert.