Common Reasons Behind these Types of Sage 50 2021 Installation and Upgrade Errors: Some program files were not properly modified or installed. The program is not accepted by the operating system. Anti-virus is preventing the program to release the installation or upgrade services. We recently upgraded to Sage 50 Accounting 2021. The upgrade went well. Having an issue/question with client upgrade. We are running a Server/Workstation environment. Windows 2008 R2 (Server) and Windows 10 workstations. Currently most of our users are remote.