it would be nice if JkDefrag could check if a drive is accessible before it tries to access it.
I have now tried a memory card of my own, mounted on a folder instead of a drive letter, but it works perfectly. JkDefrag skips the disk saying "Ignoring volume 'C:\jkdefrag\memory\' because it is a removable disk". Also without a memory card. Perhaps it's an idiosyncrasy of your memory card.