If you get this error from Drupal:
Incompatible environment
The following error must be resolved before you can continue the installation process:
Multibyte string input conversion in PHP is active and must be disabled. Check the php.ini mbstring.http_input setting. Please refer to the PHP mbstring documentation [1] for more information. (Currently using Unicode library Error)
It can be fixed by adding the following lines to your settings.php file in the PHP settings section:
/* PHP.ini overrides */
ini_set('mbstring.http_input', 'pass');
ini_set('mbstring.http_output', 'pass');
Thank you to Henrik [2] for fixing this for me, Surftown accounts need this setting in order for Drupal 5 to work.