So I've been trying to play BGTutu with my wife, but we've been running into problem after problem. I've tried all the common fixes I could find - windowed mode, Async Enumeration, hamachi (even though we're already playing on LAN) - and nothing worked; always, the dreaded Cannot connect to the game session.

The thing that got us closest to playing is gameranger; there, we'll connect briefly, and then it tells us there's a version number mismatch, with wildly different numbers; depending on who's hosting, the server number is like 7.0912309 or 6.231894, and the client number is something like 102375.12348751. At first I thought it was the mods or the install order or something, but neither copying the exact same folders over to both computers OR trying a fresh install from the same installers worked. So clearly something funky is happening with BGTutu and gameranger.

Does anyone have any ideas? Either things I can try outside of gameranger, or maybe something I forgot to do in gameranger (I did make sure it's pointing to the BGTutu folder on both computers).

I ran into the same problem some time ago when I tried to play BG trilogy with a friend. The strange thing was it started happening after we'd been playing successfully for several sessions. I wonder if it's some issue with a firewall, or something?

If you know that your wife's computer is free from malware, you might want to disable all your firewalls on the computers briefly and see if the multiplayer works. If so, you know that one of the things you disabled is causing the issue, and can work backwards to isolate the issue. Before turning off your firewalls, you should preferably close all online programs, disconnect your internet cable, blow up your ISP's computers, and/or relocate to the moon.

Ok, you don't need to do the last two, but it would be advisable to avoid exposing your computer to the internet when your firewalls are down.

Okay, so I've managed to get the same error message without gameranger by unplugging the router from the Internet and disabling wifi, so the only network connection either computer has is right to the other. But now, yeah, mismatched version numbers even though I copied the exact same files over. The only difference is that on one computer, it's on drive C, and on the other, drive D. Is it at all possible that's the problem?

Did you correct the baldur.ini files to reflect the appropriate drive change/s? Assuming a TuTu installation folder of :\Games\EasyTutu\ and a BG2 installation folder (on both drives) of :\Games\Baldur's Gate 2\, your alias sections should look like this:

For the C drive
[Alias]
HD0:=C:\Games\EasyTutu\
CD1:=C:\Games\Baldur's Gate 2\data\
CD2:=C:\Games\EasyTutu\data\
CD3:=C:\Games\Baldur's Gate 2\data\
CD4:=C:\Games\Baldur's Gate 2\data\
CD5:=C:\Games\Baldur's Gate 2\data\;C:\Games\Baldur's Gate 2\data\CD5\

For the D drive
[Alias]
HD0:=D:\Games\EasyTutu\
CD1:=D:\Games\Baldur's Gate 2\data\
CD2:=D:\Games\EasyTutu\data\
CD3:=D:\Games\Baldur's Gate 2\data\
CD4:=D:\Games\Baldur's Gate 2\data\
CD5:=D:\Games\Baldur's Gate 2\data\;C:\Games\Baldur's Gate 2\data\CD5\

Yeah, I did fix that. I'm thinking maybe the problem is EasyTutu? I'm gonna try doing a manual install tomorrow or Monday and see if that makes a difference.

After trying everything and nothing working, I realized I'd forgotten all about Baldur's Gate Trilogy, and figured I'd give that a try. It works perfectly, and serves my purposes as well as (maybe better than) Tutu. So. Problem is technically unresolved, but I'm happy now.