1st . Open normally the main.exe and log in ur account ...
2nd. Right click the main.exe and click Run as...then click ok.
then another window of mu will appear
If u want another window follow again the 2nd step ..
(NOTE:I don't know if it is working in some MU's but i tried in some Private Server MU .. it is working.)
Done!
DON'T FORGET TO PRESS THANKS IF I HELPED !