Is there anymore information that you can give us, such as what version of Mac OS and Jaksta you are running?
Have you tried doing a full reinstall at any point? If there is something broken in the programs processes that is causing it to crash then a full reinstall should reset everything.
What you will need to do is delete the app (uninstall) from Applications instead of just reinstalling over it. Then in Finder go to the top menu and then access Go > (holding one of shift/alt/control/command) Library > Application Support > Jaksta OR Jaksta Media Recorder and delete that folder (NOTE: doing this will erase your library file list in Jaksta, but your downloaded/converted files will remain intact). This folder and its files may already be deleted when the app is removed, but it's a good idea to double check and be thorough in case it remains and is reused when the app is reinstalled. Reboot the Mac and then do a reinstall of the latest Version 1 build available (http://download.shedworx.com/jaksta/beta/1.5.1_00/Jaksta-1.5.1.pkg) and it will regenerate a new copy of the deleted folder and the application files.
See how you go with a reinstall and let us know if the problem continues, and then attach a screenshot of it as well.
App freezes when I open it. Always.