Go into Level Properties and try playing with the three numbers in "Level positioning," maybe? My best guess is that you're trying to run a LEVEL#.000 with resources from .002 or something, in which case changing the next world number to 2 instead of 0 should make the level run. In general, you should always use the blockset with the same extension as the level you're working on, to avoid problems like this. That said, I'm not actually sure if that's the problem based on reading your posts, since you're leaving out crucial information and you still aren't uploading the file that's giving you trouble even though it should be less than 5kb.