From what we here at CompanionLink can tell, some of the Samsung Moment phones are being shipped with ‘USB Developer Mode’ enabled which prevents the phone from being connected via USB. This prevents many software applications, including CompanionLink, from operating correctly.
Fix: On the handset, open Settings->Applications->Development. Make sure all boxes are unchecked. Restart the phone, then connect the USB cable. The phone should now mount when connected to the PC.