Still having problem launching classic wow after patch

Hi there my dear friends, I live in Taiwan and playing classic wow in traditional Chinese version.
Before the patch on Dec 10, 2019, I used to multibox 3 toons in Classic wow with Isboxer without any problem, but unfortunately after the patch I could no longer launch the game anymore. I have tried many way, included update the isboxer software, remove the isboxer and reinstall it, reset the configuration etc.
I can launch the game smoothly out of isboxer, even under isboxer I can still run the world of warcraft classic client. But everytime when i tried to launch isboxer character sets, its a failure, and i got the BLZ51901016 error code.
Can anyone with similar experience give me a hand please, thank you most heartily in advance.
Sincerely
Richard fu.

[bob]

The only thing that changed in the patch, that we know of anyway, was that for classic, wow.exe was replaced with wowclassic.exe.

If you happen to have a game profile at the top of the Innerspace menu that runs WoW Classic successfully, then you should verify that each applicable character in the toolkit is also pointing at that same Game Profile. See https://gfycat.com/PoliteQuaintHedgehog

You can also verify that when you launch the team, that the correct exe is being used. You can see this in the Innerspace Console. Right click Innerspace, select Console, close the patcher window that sits over the top, and then launch the character set. The console will output what it is loading.

Other than that, you will need to check your config-charname.wtf files, and verify they are pointing at the correct portal.

ISBoxer itself does nothing with any of the connection between the game and the game server, so any errors reported by the game client like this are something to do with the executable being executed or the configuration it is using.

The most obvious test would be to go to your wow classic folder, run the wowclassic.exe directly, and see if you can log in. If you can, then the issue is more than likely in the config-charname.wtf files.