FAT SD card "cannot be modified"

I have a 2 gig SD card that will work on one computer, but no others. On my iMac, everything is fine and dandy, but I have Read-Only privileges on my other OS X and Windows machines.

I need to use it across platforms, so I reformatted it to FAT (MS-DOS) file system. Unfortunately, this didn't solve anything :/

I repaired the disk, but that didn't change anything either. I would like to try repairing the disk permissions, but that option is grayed out.

Honestly, I have experienced this problem over and over again with every flash drive I've had and used with my macs, and the only thing that ever works is to reformat them to Mac OS Extended Journaling system, and unfortunately, that format is simply not recognized by Windows 7, Vista, XP, etc., etc.

Help would be appreciated. Thanks!

The "Magic Key" to formatting SD or flash media to FAT is not to use Disk Utility to do the job. Disk Utility defaults to the "GUID" scheme when formatting to MS DOS format. That creates a 200 MB EFI partition on the drive which makes it useless for using it with a PC.

There is a way to use Disk Utility and format the drive correctly - it requires setting the "Options" tab to "MBR" versus the default "GUID". Or, use Disk Manager from Windows to do the formatting.