According to a Reddit post this is either caused by not setting the environment variables (there should be a readme file) or MCP trying to connect to a nonexistent server (they mentioned going in offline mode, at least to decompile; MCP has changed it website at least once in the past). Otherwise, this is the only result I got when searching for this particular error for Beta versions of MCP, and even if it works I don't know if MCP will be able to copy the required files since they changed the structure of the .minecraft folder for the 1.6 release (the game files used to be in a "bin" folder, older versions of MCP also won't know what to do with profiles, versions, or the json files that list all the libraries that the game needs).
MCP, at least as of 1.6.4, also wants you to put the server.jar in although it isn't required and I omit it to save time when recompiling (it complains that it can't find it but the client works. Official server jars are not available for older versions, which require separate mods for the server/client since they did not integrate the server with the client (singleplayer) until 1.3).
The other error is caused by the decompiled files not existing; you can't run the game until you've decompiled it and recompiled it at least once with no errors (I'd suggest making a backup of the sources once you've successfully done so so you don't need to decompile again to start with a clean installation; I've been using the same MCP installation since 2014 so I'm not sure if even the 1.6.4 version still works properly with the changes to the launcher profile file since then; an older version of AMIDST that I used to view changes to biome generation stopped working with the 2.0 version, luckily a newer version that still accepts modded jars does).
To use older versions of minecraft, you also need to use older versions of minecraft launchers in order for them to work
Old beta 1.7.2 exists in current client for you to chose and play so check that out.
If youre looking to play multiplayer make sure your client version is the same as the server version.
You cant play minecraft version 1.2.5 on a 1.9 server, or vice versa,
Also some older minecraft versions dont even have multiplayer server options (some do have LAN, but not server multiplayer)
Rollback Post to RevisionRollBack
I don't like giving too much info about the seeds i share. I feel like its better to let others explore and find out the chest contents,dungeon places and biomes. If someone is giving me a gift i would rather not know what it is until i open it for my self.