The "There is an error in the XML document" error may be displayed on startup.

As GN4 client does not display connection error details, the way to attempt to find out what happens is to run Fiddler, and to check the response of the last executed command. GN4 related commands typically contain GN4 somewhere (or the name of your GN4 application, if different).

As the responses are typically encoded, you may need to transform them into a readable text.

In order to understand the response content, you need to be familiar with SOAP and REST syntax.

Should you need support on this, save the sessions in Fiddler (File > Save > Save All Sessions - typically stored in C:\Users\<your logon name>\Documents\Fiddler2\Captures) and mail the SAZ file to the Tera support with the description of the problem you are encountering.