Teleport Interface doesn't work

I am trying to play Infdev 20100227 and use the hack interface to teleport myself. 

Unfortunately, 90% of the time (this bug doesn't seem to occur OCCAISIONALLY, but a majority of the time it happens), when I load into a world the position co-ordinates all show "Null" and when I try to teleport I get a pop-up saying "Exception Occured! java.lang.NullPointerException null"