My theme desactivates often! possible reason??

hi, mi theme at iphonerat.com
constantly desactivates, (the original wordpress theme takes place of it) i dont know what to do, i have to be checking every day to see that my blog is working ok.
which could be possible reasons? how can i solve this? i don′t want to change theme, it′s customized by me.
thanks!
sorry for my bad english ??