It may happen that the tasks tab in the web client doesn't show any task and does not even show the message
"You don't have any task currently"

Most likely on the server the file C:\ProgramData\DocuWare\ServerConfig\dwmachine.config is missing or is corrupted. This file is generated automatically on every server as soon you run DocuWare Server Setup. It is used for internal communication.
In order to re-create this file (delete the existing one) just run DocuWare Setup. Do not modify anything while running the Setup. So don't add or remove any component, just finish the Setup. The dwmachine.config should be there afterwards.
Restart the DocuWare Application Pools in IIS.

It does not work if you just copy the file from another server/pc, because the information stored in that file are related to the machine. So it is necessary that the file is generated by DocuWare Setup.