Default port for webservers to listen to http requests is 80. If you are setup to use another, you need to signal that to sh404sef, otherwise you'll experience some weird urls like : /mywebsite/http:/localhost/mywebsite/index.php

It is not uncommon to use such setups when developing on a local computer to use non-standard ports like 8080 or 88 for instance. This is recognizable to the fact that you'll have :8080 in your normal Joomla urls like so : http://localhost:8080/index.php?option=com_content&.....

To allow sh404sef to operate properly under such circumstances, you need to :

• Go to sh404sef configuration, with Extended display on
• Switch to the Very adv. tab of configuration
• Locate the line that reads
  $shDefaultParams['sh404SEF®_USE_NON_STANDARD_PORT'] = 0;
• Change it to
  $shDefaultParams['sh404SEF®_USE_NON_STANDARD_PORT'] = 1;
• Save configuration as usual. No need to purge urls for this to take effect