i broke the g string while fingering a minor
.... yay - shows how bored i am at work if these are teh kind of posts i'm making doesn't it.
like aschleman said check the string guage, but also make sure you're using appropriate strings, i think some strings are marketted more towards electrics then acoustics and thus mite be screwing you around.
Apparently you're supposed to replace your strings once a month anyways (i do it once every 3 months, but then again i don't gig as yet so i don't worry about impromptu string breakages).