New Members unable to register

[vidmarc]

I've just realised that since upgrading to 3.8.5 we've had no new member requests. I've just attempted a test signup and all is well until clicking the form submit button:

Server error
The website encountered an error while retrieving http://www.site-url/forum/register.php?do=addmember. It may be down for maintenance or configured incorrectly.

Here are some suggestions:

Reload this web page later.

HTTP Error 500 (Internal Server Error): An unexpected condition was encountered while the server was attempting to fulfill the request.

Any suggestions?

[vidmarc]

I just disabled the plugin "vbStopForumSpam" and it now works fine.