If Freeway crashes when previewing or uploading then it's possible that you have a corrupt image somewhere in your site. The first thing to try is to go to the Edit>Resources menu and in the dialog that appears click the Resample All button. This will fix any damaged references to the images used in your site. It will happen silently (i.e. with no progress bar) but should only take a few seconds.
If this doesn't fix the problem check the progress bar that appears while publishing, previewing or uploading to see if the crash occurs in the same place every time. If it does, relaunch Freeway, open the site and turn on Graphics Preview in the View menu. This will force Freeway to create and display the same graphics that it uses in the output.
Once Graphics Preview has been turned on navigate through each of the pages in your site; if there's a corrupt image on the page you're on Freeway should crash again. Once you've found the page turn Graphics Preview off and navigate to it, remove all of the images (make sure you have the originals first) and add each image one by one, turning Graphics Preview on and off each time. When Freeway crashes you've found the culprit, open the original up in Preview and save a new copy by using the Save As option. Import this new version in place of the old one.