I have the same problem on both Ubuntu and Windows.
I was previously trying a 16Gb SDCard with version 0.4.109 (I think) and that failed to detect the card. I was told it would only support 2G cards, so I went and bought one (even though Sony was able to read books copied manually onto the 16Gb card).
Now I see Calibre doesnt recognise the 2Gb either, even after upgrading to v0.4.112
I can send to main memory no problems, and also copy to the card manually, but neither of these options are ideal
Thanks