If the Sophos antivirus software fails to get installed on your computer, the error 1721 may occur. It is an installation failure error that occurs due to various reasons. Check the log details to get a clear idea about the attempted installation. If you want to know the correct reason for installation failure, check the installation logs to run an analysis and check which components have caused the error.
The error may also occur if the uninstallation process of the Sophos antivirus software fails. Otherwise, the runtime error 1721 occurs when the antivirus software fails or crashes while it is running. You may find it annoying when the error appears on the screen as the error pops up without any warning. Proceed with the steps that are given below to fix the Sophos antivirus error 1721.