Hi Miguel,
Sorry for the delay!
First can you make sure you have the latest version:
https://www.jaksta.com/download/mac/jaksta-converter
The next time this occurs, can you send your log file to us? You can find the log by going to File|Reveal Log File in the menu.
Thanks,
Ben
Jaksta Support
Miguel Lameiro
Jaksta suddenly stopped working and always crash´s when it starts to rip the video files... Why?