trying to “Empty Spam” – getting Error 500 Internal Server Error

Hi, I noticed my database was growing too large, and then discovered I have 30,000+ comments marked as “spam” but not permanently deleted. I believe this is obviously the problem of my too-big database.

However, when I go to “Empty Spam” all I get is an Error 500 Internal Server Error.

If anyone can help me with this, it is appreciated!