QuickBooks POS Error 121 occurs when you sign in with other than the 'System admin. If you still on an older version then most likely you are at a higher risk of encountering errors like QuickBooks POS error 121 installation. As we know any software is prone to errors, so QuickBooks POS. QuickBooks Point of Sale application is a power software that is good enough to take your business on a growth curve. At times, the software users report of QuickBooks Pos Error code 121 Upgrade 2020. How to fix QuickBooks Point of Sale Error code 121 Permission denied easily . Call ☎+1-800-993-4190 technical Support Help for QuickBooks.