Hi,
The mojoPortal Data layer for MySql does not use the ODBC driver for MySql, it uses the .NET Connector for MySql.
And the only way it can work in most medium trust shared hosting is if the host has the correct version of the MySql.Data.dll (the .NET Connector) installed in the GAC (Global Assembly Cache) on the server. In full trust it can use the MySql.Data.dll that is in the /bin folder but in medium trust the correct version must be in the GAC.
Bottom line is if you have medium trust hosting you will have an easier time with MS SQL database.
Hope it helps,
Joe