I can not visualize the main page of the script, but if I can enter the administration section, looking for a bit through the forums I found that you should edit the mod_rewrite and is AllowOverride set to All settings but I do not know how to do it.
Someone with this same problem that can guide me.
<Directory /path/to/your/shortener>
AllowOverride All
# … other settings …
Within the <Directory> block, make sure that the AllowOverride directive is set to All . This allows the use of .htaccess files in that directory.
After making the changes, restart the Apache server to apply the new configuration.