space available on my 256 Kingston SD

Hi folks...

I'm trying to pack in some files for my trip (at 4:00 am tomorrow!) and
can't manage to get them all to fit. The last file is 41mb. The Kingston
256mb card shows 72mb free, yet when I try to move over the 41mb file it
can't 'fit' the file into the 70mb available.

This isn't the problem of me not realizing now much space is truly on a
256... I'm reading remaining available and not even approaching that size
yet still failing to move in a much smaller file.

FWIW I'm trying to move the file over WiFi using Resco Explorer since I've
left my cable at the office and would actually like to get a couple hours
sleep before the drive to the airport.

Thanks!

Terry

slight update... actual available space is really 77.9mb so I've got even
more 'available' than I thought.

ARGH!

Any solutions most greatly appreciated.

Terry