I need help real quick.

Last night, I came to discover that you see the parsererror sign now when someone tries to send a Private Message on my website.

Hours before that, there was no problem, it was working fine. Now it doesn't.

I did experimenting and deleted a use Avatar and replaced it with a different image of the same exact file name, that's all. But last time my parsererror was caused was because of a third part javascript, could someone help me?

--UPDATE--

When a user replies to a message, it takes them to 500 PHMTL page. I already also uninstalled and reinstalled the Mailbox plugin, and it's still not working.