Hello -
I'm sorry. By unpack I of course mean, "Double clicked the little box with books in it." Once I do that, I set the path where I want the files, like where you said, and then it follows the path in my fist post.
And yes, I'm patched with the ToB version.
You are using patch 26498, and not the beta patch? You haven't used a no-CD crack on your game EXE or anything like that?
Basically, the installer is looking for
bgmain.exe in the folder you specified as your BG2 folder. It knows *exactly* what that (patched) file is supposed to look like. If it doesn't find it, or if it finds it but doesn't recognize it as a 26498-patched EXE, you'll get the message you're reporting.
If you don't think you've done anything fishy with your game EXE, you should probably try backing up your BG2 saves, uninstalling BG2, deleting its folder, and then reinstalling BG2/ToB and reapplying the 26498 patch.