You are not the only person having trouble with that SD card breakout board.http://forum.arduino.cc//index.php?topic=193520.0
Those boards do not have a logic level converter, so the SD card gets 5v from the Arduino into its 3.3v inputs. Your probes may have just enough capacitance to keep the clock (SCK) from reaching 5v.
I know the site says it is 5v compatible, but I don't see how. SD cards are 3.3v devices.
edit: Do not be fooled by those resistors (R1 to R4) on that board. Those are not voltage dividers to lower the input voltage. They are weak pullups connected to the 3.3v power bus. I attached the schematic to this post.