Thanks for sending me all the login info for your server. I discovered two new threats that had infected all your themes, these were causing the 500 errors on your site. I was able to add these new threats to my definition update and my plugin has now removed them from 36 files on your site that were found to be infected.
Your site loads fine now and is no longer flagged as infected by sucuri. Please let me know if there is anything else you need.