Your DataProviderString parameter is incorrect for connecting to MySQL. Npgsql is the name of the ADO.NET provider for PostgreSQL. You need to download MySQL Connector/NET and then locate the MySql.Data.dll assembly. You can get the AssemblyName using the System.Reflection.AssemblyName.GetAssemblyName() method. ConnectionType and AdapterType are just the fully-qualified names of types in that assembly. My DataProviderString ends up looking like this…
DataProviderString={AssemblyName={MySql.Data, Version=6.7.8.0, Culture=neutral, PublicKeyToken=c5687fc88969c44d}; ConnectionType=MySql.Data.MySqlClient.MySqlConnection; AdapterType=MySql.Data.MySqlClient.MySqlDataAdapter}