Take a look through some of these posts > http://www.google.com/cse?cx=partner...tud&gsc.page=1
Broken studs are not uncommon. I hope you aren't using any rubber or resilient material in your mounts. That will increase your chances of fastener failure. Also don't overtighten things. That can get you into trouble too. Sorry we didn't get to you before you drilled your frame. There are better ways.