The problem occurs our side, but it is THEIR issue. It is down to how the software is coded, and this is not something players can fix from their end. The cause seems to (yet again) be a faulty MGS update, one of half a dozen they insist on pushing out every month. The error message is worse than useless, saying "an error has ocurred, please contact support". It is clear support can do nothing about it, and the lack of information in the message gives them nothing they can pass to their tech team.
I have found that logging out and closing the casino, and relaunching it purely to make the withdrawal often works. It seems to be a degradation caused by being logged in and playing for some time, hence is a problem with the client software doing something that corrupts part of it during a long session.
This problem seems to have gone away for me, but I still find some MGS casinos, GNUF in particular, will freeze and lock up when exiting a game, and showing only a white screen with "....is not responding" shown in the window. It can then only be closed down by task manager.
I also get at random "game launcher/viper component has encountered a problem and has to close". This sometimes causes the lobby to close, leaving only the game I am playing, which carries on fine until I have had enough and close it down.
The problems began when MGS added this extra "games you might like to play" step when closing a game. It seems it is this step that causes the crash, even if "do not notify for 1 day" is selected. There is no option to turn it off completely, which may solve the problem. I think this because it is this that is replaced by the white screen, along with the "casinogame" task associated with the game hanging, which in turn freezes the lobby.
I also find the Witches Wealth game ALWAYS freezes at the point of exit, but unlike the others, it does not crash the casino, but the game cannot be closed normally, but if the lobby is brought to the front, Witches wealth will then close from the "x" on it's tab.
I can guarantee that GNUF will crash several times like this in the course of a session, so would be the best casino to check any solution against.
The newer Flash casinos are even worse than the old, with mind numbing lag between spins. I avoid playing Flash because of this.