Id copy things off the stick that you need, and then reformat it. (using Disk Utility, Erase->FAT32 format)
this will probably fix it for a while.
also id suggest, if its the supplied stick, then aim to replace it with another one - you can pickup these micro sticks pretty cheaply. (go for a decent brand, like sandisk) … also go for something larger e.g… 16gb (not insanely large), this gives more space to allow for overwrites etc, without fragmentation.