If you are having trouble connecting Remarkety to Magento version 1.8.0, this might be due to a bug in the installation and upgrade of Magento.
The problem is in the table which stores the password for the API user - one of the columns is simply too short, and so the encrypted password gets stored improperly.
The fix is easy, but you need access to the actual database (via phpMyAdmin or any other administrative tool).
Run the following SQL statement on your database:
ALTER TABLE `api_user` CHANGE `api_key` `api_key` VARCHAR( 80 ) NULL DEFAULT NULL COMMENT 'Api key'
You'll then need to reenter the password for the XML-RPC user in the Magento admin area.