I can't do it on omen, even when I changed it to .dat, anyone have any ideas?
Edit: I get a "Unable to find the level class. Check whether minecraft-server.jar is in your classpath." message, although I do have minecraft-server.jar.
What works for me is to convert it from .mine to .nbt and back to .mine. A long workaround, but it works. No changes whatsoever. Use the tools that are on this forum. I'm guessing this method reverts it back into some older format OMEN can use.
Edit: I get a "Unable to find the level class. Check whether minecraft-server.jar is in your classpath." message, although I do have minecraft-server.jar.