Attempting to access a company file in multi-user mode is the most frequent cause of QuickBooks Error Code 6210. It indicates that QuickBooks cannot access the company file. In order to resolve this error, you might need to examine network connectivity, ensure the proper file access rights, or rebuild QuickBooks installation. Read the complete blog post "How to fix QBCFMonitorService Not Running" for immediate assistance, or call an expert at (855) 738-0359.