When a user tries to open a company file but the file is already open on another workstation in single-user mode, QuickBooks error 6190 and 816 are typically triggered. "QuickBooks is unable to open this company file," reads the warning that appears when QuickBooks error code 6190-816 occurs. The QuickBooks error code 6190-816 indicates that the user cannot access the company file in QuickBooks. Stay tuned to the end of this post to learn more about QuickBooks error message number 6190-816, its causes, and possible fixes.