A common problem that arises when numerous users attempt to access a company file in single-user mode or when the company file is corrupted is QuickBooks Error 6210. Inadequate network configurations, out-of-date QuickBooks software, or security software interference can possibly be the cause. In order to resolve this issue, you should first update QuickBooks to the most recent version and use the Verify and Rebuild Data tool to fix any corrupted files. Make that QuickBooks is not being blocked by your firewall or antivirus software, and that multi-user mode is set up properly.