by VanessaE » Tue Jun 18, 2013 22:14
Try clicking one of the icons on the lower left corner of the Minetest window, to select the game mode that your world goes with.
Check the world.mt file inside your world's folder, look for the "gameid = " line near the top. If it says "survival" or "build", change it to "minetest" as those two have been re-combined into the main game. Then restart the program and try to access your world again.
If it isn't "survival", "build", "minetest", or "minimal", then it's for a third-party game. In that case, do not change the line at all. Instead, go get the latest version of the game mentioned there, or copy it over from your previous install.
Restart Minetest after making any of these changes.