Hello you must provide a SS , why your being auto close. So that we will see what's the problem.
Or maybe while you are still loading you keep pressing the enter button on your key board?
hmm i've also experience that before
i just did the following:
1. reinstall your infinityMu.
2. After reinstalling infinityMu. delete the infinityMu Installer(why? because my anti virus detect infinitymu installer as a virus so i decided to delete it. )
3. reinstall your wtfast ( If your using wtfast or any third program that will lower your ping )
4. Scan your whole system computer
5. restart your computer and your modem.
6. try to play and observe if your mu client will auto close again.
i hope it will work to you
update us if its work to you.