VERIFIED SOLUTION i
The Task Processor is trying to use the “Guest” account on the server where it has been installed, despite the fact that a dedicated user account has been created and specified for the Task Processor. You can verify this by checking the Event Viewer. During the installation Confirm will throw an error message stating: “Server not found. Verify that the specified server exists. The server name can not be empty”. This becomes a problem since the Guest account is usually disabled on the server for security reasons in most major organisations.
This is a known issue and the problem sometimes occurs when the Confirm Task Processor installation tries to set the Domain User name and Password on the machine when the installation is carried out using a local user.
ResolutionUPDATED: September 18, 2017
The workaround to this problem is to finalise the installation without specifying a user and then changing the Task Processor user for the Service manually to the intended user through Services.msc.