Posted 09 February 2013 - 10:54 PM
I run into this from time to time. Not sure what causes it, but some theories include lag, both server-side and user-side, changing prices as you are attempting to sell (IE you are trying to sell it to a buyer that no longer has their order placed cuz it was filled by someone else), and occasionally some issues with the user account interaction with the BLTC (this happens to me occasionally when I attempt to open up the BLTC and try to interact with it before it really finishes getting itself loaded up and open, doesn't register my gems or pull up the things in my inventory, but its an easy fix).
Theories though, nothing really substantial that I could find without taking a nice long time to search through the official forums.