spur

I'm trying to get the SD card to work but having some trouble. I'm getting a CLR_E_INVALID_DRIVER exception:

#### Exception System.IO.IOException - CLR_E_INVALID_DRIVER (1) ####
    #### Message: 
    #### Microsoft.SPOT.IO.NativeIO::GetAttributes [IP: 0000] ####
    #### System.IO.FileStream::.ctor [IP: 005c] ####
    #### NetduinoPlusWebServer.Program::Main [IP: 007c] ####
A first chance exception of type 'System.IO.IOException' occurred in Microsoft.SPOT.IO.dll
A first chance exception of type 'System.IO.IOException' occurred in System.IO.dll
An unhandled exception of type 'System.IO.IOException' occurred in System.IO.dll

I have a 2GB card, formatted to FAT32. Netduino plus is running 4.1.1 Alpha 3.

This is the code I'm trying to run:

FileStream fs = new FileStream("\\SD\\test.txt", FileMode.OpenOrCreate, FileAccess.Write, FileShare.None, 512);
StreamWriter sw = new StreamWriter(fs);
sw.WriteLine("hello from netduino");
sw.WriteLine("done.");

Exception is thrown on the first line. I haven't been able to find anything about the CLR_E_INVALID_DRIVER exception, so I'm not sure what to try to fix it. Unfortunately I don't have another micro SD card to try.

Any suggestions?