Is the SD card's write-protect switch on?
This seems like a question for the RPi forums, since the SD card works fine with your Arduino and Linux system. They might be able to help you better.
Open the phone dialer, dial *#9900# and select the 2nd option "Delete dumpstate/logcat" in the prompted menu. Select ok to 'Delete Dump' and hit exit. This will restore heaps of storage space by deleting all the log files in the device memory.