what build it your isboxer toolkit?
are you using cracked or paid?
how many character sets in total you have?
how many expansions you multibox at? basicly do you have haracter sets for more than 1 expansion?
how many characters roughly are in your character setups?
there is a reason why i ask this.
like 1-2years ago i wanted to test how much my pc can handle so i made 100 characters and launched them all up. it was fine at 1st but after that i had to clean up both wtf file within wow folder and isboxer character sets as i noticed the lag from software, like broadcasting damn slow on slave windows, so were keymaps at some point.
as for different expansions, 3-4months ago when i was trying new tbc realm, when i made character setup on tbc while having some on wotlk, launching and playing new chars on tbc was rather hard at start due to some wierd lag. i got it to work swiftly somehow, i dont know atm, maybe i cleaned it up again.