[taliesin3x3]

Here's one I figured out tonight and I hope it can help heal some heads which have been banging off walls.

A few of my forum users could not access the forum at all.  The initial page they visited errored out with a 500 SERVER ERROR.  Consulting the logs, I find out that the reason for the error is Premature end of script headers: index.php

It turns out that it is ISP based.  If your IP has no reverse DNS entry, the hostname lookup function in SMF takes too long.  Dreamhost must be pretty strict with their execution times, and they terminate the script before the (non-existent) reverse lookup finishes.

So - I disable the hostname lookup option in SMF's Server Options and all is good.

So, if any of your users don't have a reverse DNS entry, logins and such will potentially by very SLOWWWW...  and your web host is strict about execution times (like Dreamhost obviously is!) it could fail altogether.

I hope this helps someone, somewhere

[Arantor]

Thanks for posting, it's good to have such clarifications on things like this

[Ho0ber]

taliesin3x3, you are a godsend!

I had exactly this problem and was tearing my hear out! One and only one of my users had this problem, and I had come up with all kinds of crazy scenarios to explain it, but the server logs never lie!

For the record, I also am hosting on Dreamhost, and had exactly this issue for a user who had no reverse DNS.

Thanks so much!