The partial trust support for MySQL Connector/NET has improved rapidly throughout the 6.5.x and 6.6.x versions. The latest enhancements do require some configuration changes in existing deployments. Here is a summary of the changes for each version.
6.6.4 and Above: Library Can Be Inside or Outside GAC
        Now you can install the MySql.Data.dll
        library in the Global Assembly Cache (GAC) as explained in
        Section 4.5.7.2, “Configuring Partial Trust with Connector/NET Library Installed in GAC”, or in a
        bin or lib folder inside
        the project or solution as explained in
        Section 4.5.7.3, “Configuring Partial Trust with Connector/NET Library Not Installed in GAC”. If the
        library is not in the GAC, the only protocol supported is
        TCP/IP.
6.5.1 and Above: Partial Trust Requires Library in the GAC
        Connector/NET 6.5 fully enables our provider to run in a partial trust
        environment when the library is installed in the Global Assembly
        Cache (GAC). The new MySqlClientPermission
        class, derived from the .NET DBDataPermission
        class, helps to simplify the permission setup.
5.0.8 / 5.1.3 and Above: Partial Trust Requires Socket Permissions
        Starting with these versions, Connector/NET can be used under partial
        trust hosting that has been modified to allow the use of sockets
        for communication. By default, partial trust does not include
        SocketPermission. Connector/NET uses sockets to talk
        with the MySQL server, so the hosting provider must create a new
        trust level that is an exact clone of partial trust but that has
        the following permissions added:
- System.Net.SocketPermission
- System.Security.Permissions.ReflectionPermission
- System.Net.DnsPermission
- System.Security.Permissions.SecurityPermission
Prior to 5.0.8 / 5.1.3: Partial Trust Not Supported
Connector/NET versions prior to 5.0.8 and 5.1.3 were not compatible with partial trust hosting.