It's normal for some cameras to write some hidden files on a memory card. For example, these are relatively common with some camera models:
You've already got your images from it, right?
If so, I'd format the card using the camera's menu choice for format (not your PC) and see if that solves the problem. If not, try formatting it using your PC. But, make *sure* to select FAT from the drop down list you'll see as the file system type for a 2GB or smaller card (as Windows will try to format one using FAT32 by default, which is not compatible with many camera models). Then, format it using the camera's menu choice for format before using it again.
As a rule, I always reformat my memory cards using a camera's menu choice for format prior to every reuse. That insures that I always start out with a fresh File Allocation Table on the card, just the way the camera expects it, since it's performing the format, and that also creates any hidden files and folders the camera may want to see.
You'll find a CARD tab with a FORMAT choice under it in your menus: