If you are having problem with the app starting up, the first thing to do is to reboot the device. Due to the way the iPhone OS works, their built-in apps can start using more and more memory, leaving not enough for apps like ThumbJam. It is very simple to do:
Holding down both the home and the top button together for about 10 seconds. The power off
slider will come up, but don't use it, keep holding the two buttons
down until the device powers off. Then start it back up again with
the top button.
If you continue to have issues, please submit a crash report with the following instructions:
http://thumbjam.com/node/80