Usually caused by network problems, an erroneous file extension, or insufficient folder permissions, QuickBooks Error 6000 When Opening A Company File. Server-related issues or corrupted company files could potentially be the cause. Checking network configuration, renaming.ND and.TLG files, and confirming folder permissions are all part of troubleshooting. Call our QuickBooks Experts Team at 1-855-526-5749 to speak with someone as soon as possible.