EM Library: CIDs are not updating and the warning 'checksum error in file %filename%' appears in the EM Library log

Issue
EM library is not downloading new packages. When you check the EM Library log, you find warnings such as 'EM library update task succeeded but there were exceptions - Checksum error in file %filename%'.

Sophos product and version
EM Library

What to do

The proxy cache may contain a file with a corrupt checksum.

1. Clear the proxy cache by deleting the files in %ProgramFiles%\Sophos Enterprise Manager\Library\Files.
2. Attempt to download new packages.
3. If you still cannot download new packages, in EM Library, select a new Parent (such as latest-3 or central-3) and then try to download again.
4. If that doesn't work, in EM Library, right-click the EM Library icon in the tree and select 'Download from Parent (Checksum all files)'.
5. Finally, if you are still not able to download new packages, check your network to ensure that there is no equipment that may manipulate web traffic (such as a firewall).