0x7D is also send if a ladder char tries to join a non ladder game.
The shown error is decided in the client (either for ladder or non ladder)
case 0x7d:
if (D2IniData_multiplayer->isLadder == '\0') {
// Unable to enter game. A Ladder character cannot join a game created by a
// Non-Ladder character.
uVar12 = 0x2ab2;
}
else {
// Unable to enter game. A Non-Ladder character cannot join a game created by a
// Ladder character.
uVar12 = 0x2ab1;
}