. The problem was it was trying to access the document in a folder that had a bad rewrite directive (that I was using for testing) and it meant the server couldn't get to the 500.html file. 
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I have a number of custom documents for 404, 403, etc, but it turns out for some reason, apache can't find the 500 error document and it affects all my vhosts. I was setting up some error docs today, and when it came to testing the if the 500 error doc was working, it gave me the standard apache internal server error message followed by:
Quote -
Additionally, a 500 Internal Server Error error was encountered while trying to use an ErrorDocument to handle the request.
I had my syntax checked by people in freenode/#apache on irc, they said its fine, and they can't see what the problem is. All the error docs have the same permissions and are owned by the same user.
This is what my typical vhost entry looks like:
CODE
<VirtualHost 69.93.127.152:80>
ServerName zer0day.com
ServerAlias www.zer0day.com
DocumentRoot /wwwroot/htdocs/zer0day
ErrorLog "logs/zer0day-error_log"
LogFormat "%h %l %u %t \"%r\" %>s %b \"%{Referer}i\" \"%{User-Agent}i\" com$
CustomLog logs/zer0day-access_log "combined"
ErrorDocument 404 /404.html
ErrorDocument 403 /403.html
ErrorDocument 401 /401.html
ErrorDocument 500 /500.html
</VirtualHost>
ServerName zer0day.com
ServerAlias www.zer0day.com
DocumentRoot /wwwroot/htdocs/zer0day
ErrorLog "logs/zer0day-error_log"
LogFormat "%h %l %u %t \"%r\" %>s %b \"%{Referer}i\" \"%{User-Agent}i\" com$
CustomLog logs/zer0day-access_log "combined"
ErrorDocument 404 /404.html
ErrorDocument 403 /403.html
ErrorDocument 401 /401.html
ErrorDocument 500 /500.html
</VirtualHost>
I can't work out why the 500 doc doesn't work when all the others do, I can access it fine if I go directly to the doc via my web browser.
