EQ1 has had an issue like this for quite some time (years), where, for certain EQ accounts, it will not work to log in eqgame.exe directly -- only via the launcher. While outside of Daybreak we really have no idea why this occurs or why using the launchpad works properly, my guess since we started seeing this issue is that the Launchpad updates something on their end that logging in with the game itself does not, and for whatever reason it results in this kind of error whenever logging in to the account (through eqgame.exe directly).
The simplest workaround may simply be to have ISBoxer launch the launcher, instead of launching eqgame.exe directly.
You will just need to make sure the launcher closes after launching each game instance; if it stays open, your next question will be about why your Window Layout isn't working anymore, and the answer will be "ISBoxer is making them all Slot 1 because the launcher instance for Slot 1 is launching all the game instances".
So here's my suggestion:
1. Right click Inner Space and select Add Game, and point it at the Launchpad (e.g. drag EverQuest desktop shortcut to the Add Game window).
2. Adjust your ISBoxer Characters to use the added Game/Game Profile
2a. In the top left pane in ISBoxer Toolkit, under Characters, select each
2b. In the bottom right pane find the Game and Game Profile settings, and adjust to match for the Launchpad
3. Export to Inner Space
4.
Close any running instances of Launchpad (or generally a launcher will prevent new instances)
5. Launch your Character Set
5a. When the first launchpad instance comes up, log in to the first account
5b. Click Play
5c. When the game client opens, the next Launchpad instance will automatically launch IF the first Launchpad instance automatically closed. If it has not automatically closed, then manually close it, and then with the first game client still open, Launch your Character Set again to continue the launching process (it will fill in the next missing windows)
That should pretty much be it.