If you’re attempting to run an installation of PHPlist alongside Drupal you’ll find PHPlist complains about settings for magic quotes. I can’t vouch for the completeness of this fix but it gets rid of the errors without breaking anything else.
Assuming you installed the lists folder in the root of your Drupal site, you’ll find that an htaccess file in your Drupal install is changing the magic quotes values which are impacting PHPlist. You can override this for PHPlist using another htaccess file. Navigate into the lists folder for PHPlist and create an .htaccess file with the contents:
# Changes for PHPlists running on a Drupal installation php_value magic_quotes_gpc 1 php_value magic_quotes_runtime 0
Word of warning: don’t modify your host’s PHP.INI for these settings as it will likely break something else if you host multiple domains. In my case it broke WordPress so stick with the htaccess method.