No registration validation and 500 error

We just installed S2Member Pro in a development sandbox, and we’re seeing a few 500 errors from the s2member-o.php file.
It appears that it should output javascript and CSS, but server returns 500 error response instead.
We assume this is the reason no validation is occurring on our test registration page.

The errors are:
Failed to load resource: the server responded with a status of 500 (Error)
http://some.server.net/~user/project/content/plugins/s2member/s2member-o.php?ws_plugin__s2member_css=1&qcABC=1&ver=130221-130221-4063470020
Failed to load resource: the server responded with a status of 500 (Error)
http://some.server.net/~user/project/content/plugins/s2member/s2member-o.php?ws_plugin__s2member_js_w_globals=1&qcABC=1&ver=130221-130221-4063470020

This install is in a development sandbox with a URL structure like the following:
http://some.server.net/~user/project/

Additionally, we are using a non-standard WP installation structure like this:
/.htaccess -> rewrite rules for our non-standard structure
/wp-config.php
/content -> for plugins, themes, and uploads
/core -> for WP core

We have run the server s2-server-scanner.php tool to examine our compatibility.
The only issues flagged were:
[ERROR] PHP Short Open Tag: < ?
[ERROR] PHP Echo Tag:
However, we are unsure if those flags are related to the issue we are experiencing at this time.
Additionally, we are unable to enable php short tags, as it violates our development standards.

Any assistance you can provide would be appreciated.

Hi Nerdery.

Have you tried asking your web host for help to understand better what may be causing the error? Maybe their logs show a clue to solve this.

Here’s an article on another error that I don’t know if it’ll help you with this: Knowledge Base » Mod Security, Random 503/403 Errors

I hope that helps.