Quote from nostalgicleaf
I am currently using mcedit to modify a 1.2.5 generated anvil world with much success. What exactly are you having trouble with?
I realized how snob-ish my post sounded. 'Oooo, it works for me! Y u no work?'
I am running mcedit 0.1.1-32bit on amd64, 8Gb of ram, hd6870 on WIn7 Ultimate 64bit. Apparently there are known issues with the PyGL bindings mcedit uses for python 2.7 on certain Intel chips (like the crappy ones) and it sounds like they won't be fixed or updated any time soon. Head over to the mcedit thread and either go to the github links on the first page to download the same copy I am using, or head to the last page in the thread and look for the link to Zap's 64bit build (if you have 64bit OS and CPU).
If you are using Intel integrated graphics, I don't know what to say. You can pick up an HD6450 for $40?
I know this is a very old post. But I just wanted to thank you. I had chunk errors that made my world unplayable for the past 2 months. Thanks to your post I found a proper mcedit that worked on 1.2.5, I deleted the chunks and I now can play on my world again. Thank you so much.