What is the QBWin.log file or QuickBooks Log File? QuickBooks desktop stores data about the events that happen in the software in the QBWin.log file. QBWin.log is for the windows operating system & the QuickBooks log file is for MAC OS. These files are used to analyze & rectify errors in the QuickBooks Desktop company file. … Continue reading Fix QBWin.log Error: Verify Item: Invalid tax agency