[21:30:57] [Server thread/INFO]: Starting minecraft server version 1.7.10
[21:30:57] [Server thread/INFO]: Loading properties
[21:30:57] [Server thread/INFO]: Default game type: SURVIVAL
[21:30:57] [Server thread/INFO]: Generating keypair
[21:30:57] [Server thread/INFO]: Starting Minecraft server on *:25565
[21:30:57] [Server thread/INFO]: Preparing level "world"
[21:30:58] [Server thread/INFO]: Preparing start region for level 0
[21:30:59] [Server thread/INFO]: Preparing spawn area: 21%
[21:31:00] [Server thread/INFO]: Preparing spawn area: 48%
[21:31:01] [Server thread/INFO]: Preparing spawn area: 72%
[21:31:02] [Server thread/INFO]: Done (4.412s)! For help, type "help" or "?"
[21:31:43] [User Authenticator #1/INFO]: UUID of player Showdown is 27d0e766-894b-4034-bbe4-908f23d25859
[21:31:43] [Server thread/INFO]: Showdown[/75.133.231.99:61285] logged in with entity id 2548 at (-240.5, 85.0, 266.5)
[21:31:43] [Server thread/INFO]: Showdown joined the game
[21:31:51] [Server thread/INFO]: Showdown has just earned the achievement [Taking Inventory]
[21:32:14] [Server thread/INFO]: Showdown has just earned the achievement [Getting Wood]
[21:32:32] [User Authenticator #2/INFO]: UUID of player Rekto is 80b5eb5f-1e1e-42f4-a8c6-dbae59f34e0e
[21:32:32] [Server thread/INFO]: Rekto[/68.198.182.101:58260] logged in with entity id 3644 at (-248.5, 82.0, 259.5)
[21:32:32] [Server thread/INFO]: Rekto joined the game
[21:32:33] [Server thread/INFO]: Rekto lost connection: TranslatableComponent{key='disconnect.genericReason', args=[Internal Exception: java.io.IOException: An established connection was aborted by the software in your host machine], siblings=[], style=Style{hasParent=false, color=null, bold=null, italic=null, underlined=null, obfuscated=null, clickEvent=null, hoverEvent=null}}
[21:32:33] [Server thread/INFO]: Rekto left the game
[21:32:40] [User Authenticator #3/INFO]: UUID of player Rekto is 80b5eb5f-1e1e-42f4-a8c6-dbae59f34e0e
[21:32:40] [Server thread/INFO]: Rekto[/68.198.182.101:58263] logged in with entity id 3686 at (-248.5, 82.0, 259.5)
[21:32:40] [Server thread/INFO]: Rekto joined the game
[21:32:41] [Server thread/INFO]: Rekto lost connection: TextComponent{text='Disconnected', siblings=[], style=Style{hasParent=false, color=null, bold=null, italic=null, underlined=null, obfuscated=null, clickEvent=null, hoverEvent=null}}
[21:32:41] [Server thread/INFO]: Rekto left the game
[21:33:28] [Server thread/INFO]: Showdown lost connection: TextComponent{text='Disconnected', siblings=[], style=Style{hasParent=false, color=null, bold=null, italic=null, underlined=null, obfuscated=null, clickEvent=null, hoverEvent=null}}
[21:33:28] [Server thread/INFO]: Showdown left the game
[21:33:35] [Server thread/INFO]: Stopping the server
[21:33:35] [Server thread/INFO]: Stopping server
[21:33:35] [Server thread/INFO]: Saving players
[21:33:35] [Server thread/INFO]: Saving worlds
[21:33:35] [Server thread/INFO]: Saving chunks for level 'world'/Overworld
[21:33:35] [Server thread/INFO]: Saving chunks for level 'world'/Nether
[21:33:35] [Server thread/INFO]: Saving chunks for level 'world'/The End
[01:02:08] [Server thread/INFO]: Starting minecraft server version 1.7.10
[01:02:08] [Server thread/INFO]: Loading properties
[01:02:08] [Server thread/INFO]: Default game type: SURVIVAL
[01:02:08] [Server thread/INFO]: Generating keypair
[01:02:08] [Server thread/INFO]: Starting Minecraft server on *:25565
[01:02:08] [Server thread/INFO]: Preparing level "world"
[01:02:08] [Server thread/INFO]: Preparing start region for level 0
[01:02:09] [Server thread/INFO]: Preparing spawn area: 11%
[01:02:10] [Server thread/INFO]: Preparing spawn area: 27%
[01:02:11] [Server thread/INFO]: Preparing spawn area: 45%
[01:02:12] [Server thread/INFO]: Preparing spawn area: 62%
[01:02:13] [Server thread/INFO]: Preparing spawn area: 82%
[01:02:14] [Server thread/INFO]: Done (6.066s)! For help, type "help" or "?"
[01:02:39] [User Authenticator #1/INFO]: UUID of player Showdown is 27d0e766-894b-4034-bbe4-908f23d25859
[01:02:39] [Server thread/INFO]: Showdown[/75.133.231.99:49296] logged in with entity id 1459 at (-191.5, 63.0, 247.5)
[01:02:39] [Server thread/INFO]: Showdown joined the game
[01:02:59] [Server thread/INFO]: Showdown has just earned the achievement [Taking Inventory]
[01:03:00] [Server thread/INFO]: [Showdown: Set own game mode to Creative Mode]
[01:03:01] [Server thread/INFO]: [Showdown: Set own game mode to Survival Mode]
[01:03:03] [Server thread/INFO]: [Showdown: Set own game mode to Creative Mode]
[01:05:19] [Server thread/INFO]: Showdown lost connection: TextComponent{text='Disconnected', siblings=[], style=Style{hasParent=false, color=null, bold=null, italic=null, underlined=null, obfuscated=null, clickEvent=null, hoverEvent=null}}
[01:05:19] [Server thread/INFO]: Showdown left the game
[01:05:34] [User Authenticator #2/INFO]: UUID of player Showdown is 27d0e766-894b-4034-bbe4-908f23d25859
[01:05:34] [Server thread/INFO]: Showdown[/75.133.231.99:49313] logged in with entity id 23784 at (-1085.0736376707487, 109.5262025574561, -22.07339834608221)
[01:05:34] [Server thread/INFO]: Showdown joined the game
[01:05:34] [Server thread/INFO]: Showdown lost connection: TextComponent{text='Disconnected', siblings=[], style=Style{hasParent=false, color=null, bold=null, italic=null, underlined=null, obfuscated=null, clickEvent=null, hoverEvent=null}}
[01:05:34] [Server thread/INFO]: Showdown left the game
[01:06:07] [User Authenticator #3/INFO]: UUID of player Showdown is 27d0e766-894b-4034-bbe4-908f23d25859
[01:06:07] [Server thread/INFO]: Showdown[/75.133.231.99:49327] logged in with entity id 24062 at (-1085.0736376707487, 109.5262025574561, -22.07339834608221)
[01:06:07] [Server thread/INFO]: Showdown joined the game
[01:06:07] [Server thread/INFO]: Showdown lost connection: TextComponent{text='Disconnected', siblings=[], style=Style{hasParent=false, color=null, bold=null, italic=null, underlined=null, obfuscated=null, clickEvent=null, hoverEvent=null}}
[01:06:07] [Server thread/INFO]: Showdown left the game
here you go, two different logs, same server, same errors, first one was when I had a friend try to join, and when I tried to join, we both got that error, second one is from me flying around in creative on my server seeing if something would trigger that error again, which it did

I asked about this stuff on /mcg/ and the best answer I got was
This could also happen with mods - adding a slider or item slot to a GUI without changing a version number to let an older client know "you don't know how to read this message", so it tries to put a long message into a space that's too short.
Dont know if Im using the wrong version of a mod for this to happen, or if Im missing another mod that would prevent this