SD Card Fails to mount

I currently use a SanDisk Ultra 4GB SD Card (class 4 - up to 15 MB/s) for my application and it works fine. I recently tried to use a SanDisk Ultra 8 GB SD Card (class 6 - up to 20 MB/s) and the application now fails every time with the following error. I tried another 8 GB class SD card by Wintec and it worked fine. Would it be due to the high speed rating of the SanDisk Ultra 8 GB SD card? This is a production application so I was just trying to go with the highest possible quality (and quickest) SD card without breaking the bank.

#### Exception System.Exception - 0xffffffff (1) ####
#### Message: 
#### GHIElectronics.NETMF.IO.PersistentStorage::.ctor [IP: 0000] ####
#### SPSMicro2.CoreLib.SPSMicroApp::MountFileSystem [IP: 000e] ####
#### SPSMicro2.CoreLib.SPSMicroApp::Initialize [IP: 002d] ####
#### SPSMicro2.MicroUI.Program::Main [IP: 0039] ####

A first chance exception of type ‘System.Exception’ occurred in GHIElectronics.NETMF.IO.dll
The program ‘[6] Micro Framework application: Managed’ has exited with code 0 (0x0).

Which board are you using?

ChipworkX and the FEZ Mammoth mainboard.

If really need that card, we can check to see if we can improve the driver for you. Shoot me an email if interested.