number of session exceeded

hello
i'm using arcgis desktop 10.2 and sql server 2008 express in the same machine just for test when more than 3 machine try to connect to my Geodabase (sql server ) they have this message :number of session exceeded
can someone know why i have this problem knowing thati have arcgis advanced and sql server 2008 express the both accepte many connection at a time

thanks