It looks familiar to me. I'm waiting for an answer from a experienced member about my comment on that post for a more pratical solution and an explaination : SD Card on Ethernet Shield on MEGA not working - Storage - Arduino Forum
I tried the same kind of 4 Go SDHC card and 8Go micro SDHC card. Everytime I got one of those error : "SD Card Initialization Failed!", "initialization failed", "Could not find FAT16/FAT32 partition", "Invalid format, reformat SD.", "errorCode: 0X1,0X0", etc.
I tried all sketchs from the SD Library then I searched for a more recent SDFat Library and a tested 9 of the sketchs proposed. I tested with a simple SD Card module then I bought an ethernet module to give it some fresh trials without any good results except for the sketch SdInfo from the SDFat library (I still don't know why). I downloded the new 1.6.6 IDE. I made sure I was using the right card/port while compiling and the SCK, MISO, MOSI, SS pins were the right one and the code was properly filled with right pins number (no conflict with a wire too). I tried to desactivate the Ethernet controller, to change the SPI_SPEED, to format the card with Windows (apparently not an ideal solution), with the sketch SDFormatter and with the software SDFormatter 4.0. I looked at the forum for similar issues reported, tutorials, videos and also the SD and SDFat libraries in detail to understand how it's works.
After many hours playing around I found a temporary fix that I still do not understand and that I commented in the other topic mentionned above. I really hope it'll work for you too and that an other member will have an explaination for me.