When the 2x tilesets were created, some tiles were moved to new positions in their tileset and some tiles were removed entirely.
When the game sees an "old" map created before the 2x tiles were added, the game will try to fix moved or missing tiles.
The official maps were all updated to use the new 2x tilesets. If you look in each map.info file, you'll see this line was added:
When the game sees "fixed2x=true" in map.info, the game will not apply any fixes to the tiles used by the map; the game assumes the maps have already been fixed.
You can choose to leave your old maps alone, or update them to use the new 2x tilesets.
To update your old TMX files for 2x tilesets, use the Tools > Check Maps menu command in TileZed. You can check all TMX files in a directory by pressing the 'Check now" button, or check only the current map by pressing the "Check Current Map Only" button. This will print a list of tile issues that may need to be fixed. Double-click on an issue to go to that location in the map.
There's also a "Check Buildings" command that checks BuildingEd files for tile issues.
After updating your maps and buildings, use "Generate Lots" in WorldEd to test them in the game. Remember to add "fixed2x=true" to the map.info file.
@AtoxwarriorI think the "Unknown grime_wall" error is because WorldEd is trying to launch an older version of TileZed. You need to change the app that is associated with the TMX file type (so it uses the new version of TileZed, not the old one).