After installing MySQL Connector/NET 6.7.4 today, my web app failed to start. It is because some MySQL membership providers were added to C:\Windows\Microsoft.NET\Framework\v4.0.30319\Config\machine.config and the MySql.Web.dll assembly (MySql.Web, Version=6.7.4.0, Culture=neutral, PublicKeyToken=c5687fc88969c44d) could not be loaded.

Uninstalling the Connector/NET 6.7.4 makes my web app work normally again. Refer to http://bugs.mysql.com/bug.php?id=69808 for details.