I assume you are using Caché on Windows, and you are launching Terminal from the Cube on the local desktop of the PC where Caché is running.

In this case the security settings of the %Service_Console service (System > Security Management > Services) are what you need to adjust.

Enabling only "Unauthenticated" will mean that you don't get prompted for username/password, and your Terminal session will report $username="UnknownUser". But the security settings for UnknownUser will also have to allow that account to get to the programmer prompt. If they don't, your Terminal session won't start.

Enabling only "Operating System" will mean that provided a Caché user account exists that matches the Windows account you are logged into the desktop as, your Terminal session will report that username as its $username. Again, the Caché account will need sufficient permissions to get to the programmer prompt.

First, using my moderator superpowers I have moved this out of the Developer Community Feedback group (intended only for feedback about the DC platform) and into the Cache group.

The <NETWORK> error code hints that your Cache instance is involved in some ECP networking. Maybe that is having a problem. Check cconsole.log at both ends of the connection(s) for clues.

In general though, I suspect your issue is too site-specific for DC members to be of much help. I recommend you open a support ticket with InterSystems WRC.

Also, a similar kind of check using a method of %SYSTEM.Security is not case-sensitive with respect to the username:

USER>w $system.Security.CheckUserPermission("laura_test_DEV","%Development")
USE
USER>w $system.Security.CheckUserPermission("laura_test_dev","%Development")
USE
USER>w $system.Security.CheckUserPermission("laura_test_devX","%Development")
 
USER>

The priv check is case-sensitive on the username:

USER>w $system.SQL.CheckPriv("laura_test_dev","9,%Library.File_FileSet","e","USER")
0
USER>w $system.SQL.CheckPriv("laura_test_DEV","9,%Library.File_FileSet","e","USER")
1
USER>

Anyway, I'm glad it's now working for you.

BTW, to paste an image into a DC post I save it to a file, then use the following button in the DC editor to upload the file:

And then I sometimes (as above) use the Image button on the toolbar to add a 2-pixel border to the image, then the Increase Indent to move it across.