According to details and troubleshooting guides found on a forum, it appears that the most common causes of this issue are related to the wrong password, wrong box IP or no connection to the box. I recommend you check all of them, and additionally make sure that you have the latest version of the software installed as well. From what I understand you have the possibility to install the latest version right from the software using a built-in module.
Additionally, note the admin as the user and dreambox in case you need it.