There was a workaround some time ago I still use in my I2C projects.
Put it at the beginning of the project to give the port the right level. Also advice to get a Scanna Plus device from ikalogic.com to debug this type of problems in minutes.
//Workaround for a bug where you need to disconnect the I2C bevore it works. OutputPort p = new OutputPort(Pins.GPIO_PIN_SDA, true); p.Write(false); p.Dispose();