You set up a user and password in BI that you're using in the apps logon, correct?
In the LAN setting of the app, do you have something like below? BI's port must be in the URL and no port forwarding required if attempting to access via LAN.
Code:
http://Your-BI-Server-LAN-IP:BI-port
such as http://192.168.1.200:81
Lastly, can you access from your LAN the BI server's UI3 with this URL below?
Code:
http://Your-BI-Server-LAN-IP:BI-port/ui3.htm