I have been having a problem with the shopping cart on Jigshop crashing my site.
The cause in my case has been traced to the use of:
session_start() in this file:
If you replace it with:
if ( ! session_id() ) session_start();
the site works again.
It has been suggested that I raise this issue with the developers because it might be causing issues with other plugins as well.
You can follow the discussion here:
Many thanks for a great plugin.