500 Errors on Save/Publish

On Merit Solutions, we're getting 500 errors whenever you update a published post or publish a post. We've had a similar issue before on a different site, where modsecurity was at fault, but I don't think that's the issue here. When modsecurity was the issue, it was discriminant and only affected a couple of posts. This issue seems to be affecting all posts on the site.

I've provided site login credentials and FTP access. Let me know what you find.