error 500 when sending newsletter

I can not send any email with eNewsletter. When I hit the send button nothing will happen for about 15 minutes and then I get an internal server error - Error 500.
My outgoing email and bounce settings are correct. Everything is up to date. I disabled all plugins except e-newsletter and still got the same result.

This is set up on multisite, and I have granted support access. The main site I have been having trouble on is /housingguru , but I believe all sites produce the same error.