Check for a file named "smdl2tmp1.asec" in the ".android_secure" folder on your SD card and delete it.
You probably won't find that folder on your SD card with a standard file explorer (ES, ASTRO, . . ) because a period (.) in front of a folder name makes it a hidden folder to Unix and Linux operating systems. The app "Root Explorer" will work, FYI.
Either plug the USB cable in to a computer and delete the file that way or take the microSD card out and put it in a card reader connected to a computer and do it that way.