Shep_

Hi again LexManos, I bit the bullet and clicked "OK" after the long list of IDs that were mismatched between the world and game. It looks OK. Thanks! Shep_

Hi LexManos, Our posts crossed in the ether. Thanks, I'll give it a try without MobSpawnHighter, and hope for the best! Shep_

Hello again, I removed everything from the "mods" folder, and downgraded to the "stable" MC Forge installed into MC 1.5.1, version 611. The same error happens. It's "mismatch between the <something> and world items," and it still hangs my PC if I choose not to continue. FWIW, I've been installing MC Forge into MC .jar files for a while now. I'm confident I haven't messed that part up, and of course, I deleted META-INF before copying in the Forge classes (using 7-zip). If it helps, here's the pastebin from this run: http://pastebin.com/UqSxX11U Thanks, Shep_

I just upgraded to MC 1.5.1 today. I'm using today's Forge 7.7.1.676, plus the very latest ChickenCoreMods, NotEnoughItems, InvTweaks, and ModSpawnHighlighter, all for MC 1.5.1. CCC and NEI were installed in coremods, and the others were in mods. There were no other mods, such as OptiFine. I was able to log in to fyre.uk and look around. I didn't use any of the mods' features, I just explored a bit. Then I logged out, and tried to load a local SP world that I had created in MC 1.4.7. If it matters, I've shared this world on the LAN, to play MC with my wife, who until now was also running MC 1.4.7 with the same 1.4.7-appropriate modes (except ModSpawnHighlighter, which didn't have a 1.4.7-compatible version). As soon as I double-clicked the world, I got an error message in the MC UI that lots of ID's were missing or out of sync (sorry, I don't remember which), and I elected not to continue. After that, I saw "Shutting Down the Internal Server" which was basically an MC hang--nothing I did would quit MC, including Ctrl-Alt-Delete, so I had to restart to recover. Here's the ForgeModLoader log: http://pastebin.com/PDS9ULHm Thanks, Shep_

Also, have you renamed the CCC and NEI .jar files? The correct, downloaded versions don't end in "1.5.1.jar". Make sure you're downloading them from the official thread here.

Also, have you renamed the CCC and NEI .jar files? The correct, downloaded versions don't end in "1.5.1.jar". Make sure you're downloading them from the official thread here.