Error: 'Login details for 'User' login were not found in the key file'

This error message has occurred due to an update for Sophos Anti-Virus.
​
Following an update, Sophos is detecting the file FMCore.dll as a PUA and is instantly clearing it as a threat.
​
Please ask you IT to update the exceptions in Sophos for the FactoryMaster folder and re-run ClientSetup.
​
If you do not use Sophos Anti-Virus and are still experiencing this error message, please raise a new case online and reference the title of this article.