You click the place you want to put your castle, and when the circle pops up, click on the little downward swooshie arrow at the bottom "move castle".
Still trying to move. Tried several time s several different ways........this is really getting old
@RichardLionhart (US1) no, that window is a bug in the software. It comes up sometimes when you try to attack marauders, join battles, etc.
Refresh your browser and you should be able to continue play without the pop-up.