Minecraft released 1.5.2. As should be expected if you have played much on this (or any other) server, we are not quite ready to update the server yet. We’re waiting on CraftBukkit and other back-end things to be ready. DO NOT UPDATE YOUR CLIENT TO 1.5.2.
Also, creation of shops is currently blocked due to a bug. We are working on a solution. Existing shops should function normally.