Making a map? In Content Manager, DEACTIVATE ALL mods not to be used in the map editor, then restart the game entirely before going to work in map editor. Many mods are not designed to function inside the editors like map and asset editor! (An example is Ultimate Eyecandy. The map editor has a time of day slider just like UEyecandy, so the two freak out when used together). Other mods that you *think* might work or that you don't think are a big deal may very well cause some issues. The required restart ensures that the mods that require a restart to turn off are not still running, and that you avoid any issues with double loading.

If you have the wrong kind of mod still running, or run a mod that works in map editor but is actually not supposed to be active, at best they will cause you some annoying problems while making a map, at worst they can crash (losing all the work since the last save) or even break your map entirely! Before I understood this, I lost several maps, and could not even get in to fix them. They are broken and lost forever!

SO, here are the current mods I use when making maps, and the only ones I have active during map making. There may be other mods that work fine in the map editor, I'm just not interested in going through and testing everything for everyone. This is my hobby. ;)