Copied my answer from a guy talking about i/o errors to his 8 Gbyte SD card via his reader/writer that works with 2 Gbytes and lower cards fine.
I have many SD cards. My first one was 256 Mbytes, then 512 Mbytes, 1 Gbyte, 2 Gbytes, 8 Gbytes.
There is large difference between the hardware and software access to the file system on the 8 Gbyte unit because it (a) is a SDHC hardware unit, and (b) must use the FAT32 file system instead of the FAT16 file system of all of the older units.
This key difference stems from the math involved in accessing beyond the 2 Gbyte limit and the size of 32 bit integer math. This discontinuity happens because you have to jump to using either 48 or 64-bit integers to seek to byte offsets within the file system
in the larger capacity units. If you have done any programming of computers with random access file updates, you'd know that seeking in a file using a negative integer can be used to seek backwards relative to your current file pointer's location. This means
that rather than accessing 4 Gbytes like would be possible using full 32 bits, you can access +/- 2 Gbytes using file seeking with 32 bit integer variables / values. To access a larger file system, you need to update your programming to use system calls for
seeking that use 64-bits or so, then you'd be good to go on disks with sizes above 2 Gbytes.
To do this "different kind of access" you need a newer "SDHC-capable card reader" that when asked to examine the 4 Gbyte, 8 Gbyte, and 16 Gbyte SD cards being sold in stores now will correctly presume that FAT32 file system formatting and access must be used,
otherwise, using an older card reader meant for 2 Gbyte cards or smaller will result in various kinds of errors, one of which you seem to be getting now.
Some of the newer still cameras being sold starting in about mid 2007 had the capability of using SDHC memory cards, and would automatically format them correctly to use FAT32.
First I tried to buy a really cheap SDHC reader for about $4.99. It was really bad and would very seldom work properly. I took the unit back to the store, they tested it and found it was crappy too--I got one of the two cheap units to work, but they could
not get any of them to go.
I upgraded to the more expensive model SDHC card reader that was $9.99 and that one worked like a champ--completely reliable. Both of these were junky made in China units.
Additional details. I bought a network media player with USB, 10/100 UTP Lan, 2.5" drive bay, that seems to be a Linux based machine running Samba file sharing. The $9.99 SDHC card reader is currently attached with the 8 Gbyte SDHC card inserted and works
great. I just shut down the Patriot Box Office media player, then removed the card reader and plugged it into my WinXP home SP3 computer... The computer immediately reports that the "disk" just plugged in contains photos and whatnot and what do I want to
do? So I click on Cancel so that nothing stupid happens.
Seems like you have to have hardware that is known to operate correctly and reliably with SDHC sized cards?