Typo Error in installer_base.lib.php
In SVN 1999
installer_base.lib.php line 1429:
if(is_file($install_dir.'/interface/ssl/ispserver.crt') && is_file($install_dir'/interface/ssl/ispserver.key')) {
should be
if(is_file($install_dir.'/interface/ssl/ispserver.crt') && is_file($install_dir.'/interface/ssl/ispserver.key')) {
you forgot a . after install_dir