This issue can occur anytime the Notes Client is not functioning properly on the DA server. 

Launch the Notes client on the DA server and ensure that it is configured correctly by connecting to a Domino server. 

In some instances a corrupt cache.ndk file can cause this issue. In that case close Notes on the DA server and delete the Cache.ndk in the Data directory of the notes client. This file is generally located in the following directory: C:\Program Files (x86)\HCL\Notes\Data

On rare occassions the installation of the Notes client on the DA server may be corrupted. In that case uninstall and then reinstall and configure the Notes client on the DA server.