I have never seen this error before:
HTTP/1.0 500 Perl execution failed Server: MiniServ/1.690 Date: Sun, 7 Sep 2014 17:45:02 GMT Content-type: text/html; Charset=iso-8859-1 Connection: close
Error - Perl execution failed
Undefined subroutine &virtual_server::ui_img called at /usr/libexec/webmin/virtual-server/edit_newfeatures.cgi line 29.
Usually after going through Virtualmin configuration, you need to disable mailman from features and plugins before you can get a Virtualmin installation to pass. The error above is what I get when I hit the features and plugin button.
I can always try to wipe the server and reinstall. But before I do that, I wanted to see if there was an easier fix/