I think that is definitely the issue. I was having the same problems with not being able to launch mod packs at all, but after downgrading my Java to 1.6 I have been able to run tekkit lite 3 times in a row successfully.
I followed the instructions here to do that http://reviews.cnet.com/8301-13727_7-57539151-263/how-to-manage-the-java-6-and-java-7-runtimes-in-os-x/