QuickBooks Error 6143 typically occurs when opening a company file or during a backup process. It is caused by damaged or corrupt company files, improper installation, or system-related issues. To resolve this, start by running the QuickBooks File Doctor to repair file damage. Ensure that your system is virus-free and update QuickBooks to the latest version. If the issue persists, manually rename the .ND and .TLG files, then restart QuickBooks. Finally, try restoring your company file from a backup. Following these steps should effectively resolve QuickBooks Error 6143 and help maintain smooth business operations.