This article will provide you with a solution to a possible issue causing virus signature updates to fail on Windows Server 2003, with the following error message: "An invalid request was sent to the update server".
To ensure the integrity of our update process, we are using SHA2 encryption for our security certificates.
Windows Server 2003 (prior to R2) cannot natively receive certificates which use SHA2 256 encryption or higher from the Windows Update function.
Microsoft has released a hotfix for this issue.
More information on how to implement it can be found here: