просто добавете това към вашата web.config
<system.data>
<DbProviderFactories>
<remove invariant="MySql.Data.MySqlClient" />
<add name="MySQL Data Provider" invariant="MySql.Data.MySqlClient" description=".Net Framework Data Provider for MySQL" type="MySql.Data.MySqlClient.MySqlClientFactory, MySql.Data, Version=6.6.4.0" />
</DbProviderFactories>
</system.data>
<entityFramework>
<providers>
<provider invariantName="MySql.Data.MySqlClient" type="MySql.Data.MySqlClient.MySqlClientFactory, MySql.Data, Version=6.6.4.0" >
</provider>
</providers>
</entityFramework>
но не мисля, че можете да използвате 6.6.4 с EF6...