I've seen a number of sites running into this message after upgrading to 8.3 in their Webclient classic.
This will occur if the "Web Client Workgroup Server URL" field is left blank at the time of installation. If you are upgrading simply enter the machine name of the Workgroup server that you are intending the Web Client (and all users browsing to that URL) to connect to.
If you are already seeing this error, then simply modify the web config file
The webconfig file by default it is located under:
<C:\Program Files\Hewlett Packard Enterprise\Records Manager\Web Client Classic
open "hptrim" with notepad
<workgroupServer workPath="C:\HP Records Manager\WebServerWorkPath\" port="1137" name="workgroupservername"/>
Enter in the workgroup server name, if there is nothing entered after "name"