SD card example not writing

I am trying the WiKi example and it does create the file text.txt but it does not write anything on it.
I am using a 16GB FAT32 SD card.

In have also tried the data storage demo (using a random number instead of a groove light sensor) and again the file was created but it stays empty.
I tried several Sd cards … so this is either a library or a hardware issue

the example in the arduino GUI actually does something , wite somewhere … but not on the SD.
Any help would be appreciated!!!