After breaking a fence cornerpost you can't immediately pave the land beneath it. Had to either raise or lower the level by one via survey before any form of landscaping could be used on it.
W3 to W6 - Blockland. Special mentions: New Avalon, Tarn of Hotdog, Red October. W7 - Elvenia, til we all got lazy. W8 - Cult of R'lyeh, til the deeps called us back. W9 - Tartarus, til death/wizards came for the land itself. W10 - ???, ruined and forgotten.
Has nothing to do with the corner post. Most likely the tile under you CP was a forest tile or the like. Should be an error message when attempting to pave when not possible. Thanks.
"The psychological trials of dwellers in the last times will be equal to the physical trials of the martyrs. In order to face these trials we must be living in a different world."