Older devices may not be compatible with newer SDHC & SDXC SD Cards. It should be possible to repartition a higher capacity card and reformat it with FAT in order to support older devices. The additional space on the Card will be wasted, but the device should accept the Card. Here is the procedure using the Windows 7 Diskpart command line tool:
C:\> diskpart DISKPART> list disk DISKPART> select disk n DISKPART> list partition DISKPART> clean all (deletes all partitions on the drive/card) DISKPART> CREATE PARTITION Primary Size=50000 (50 GB) DISKPART> format fs=fat quick