This might be connected with SEO friendly URLs settings for Joomla.

The following steps might help to fix the issue:

  1. Connect to your Joomla website data via FTP.
  2. In Joomla base installation, find “htaccess.txt” file.
  3. Rename the file “htaccess.txt” to “.htaccess” (make sure you don’t forget to use the dot – it’s .htaccess)
  4. Login to your Joomla back end – go to Global Configuration
  5. Change  ‘Enable SEF URLs’ and ‘Use Apache mod_rewrite’ to Yes.
  6. Save the configuration.