This occurs if any processes related to your Sage software are still running on your computer when you run the installer. It can also occur if you don't use the run as administrator option.
These processes sometimes continue to run in the background on your computer, after you close your software.
To ensure it's fully closed:
Save any work you have open, then restart your computer.
When you log back in to your computer, don't open any Sage software.
Browse to the folder you saved the background installer in.
Right-click Sage50Payroll_BU_3200321.exe, then select Run as administrator.
Wait a minute or so to allow the update to complete.
Next steps
Your software is ready for you to continue with processing your payroll as normal.