Cannot Use Command Blocks and Command Block Minecarts in LAN Multiplayer on creative mode

Thank you for your report!
However, this issue has been temporarily closed as Awaiting Response.

You need to be an OP and in creative mode to use a command block. If you already are, then: we do not have enough information to find the cause of this issue.
Please force a crash by pressing F3 + C for 10 seconds while in-game and attach the crash report ([minecraft/crash-reports/crash-<DATE>-client.txt|http://hopper.minecraft.net/help/guides/finding-minecraft-data-folder]) here.

Once attached, the report will be reopened automatically.

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I don't know how to pin crash messages to reports, so im leaving it in a comment:

Minecraft Crash Report ----
// Oops.

Time: 10/14/17 5:58 PM
Description: Manually triggered debug crash

java.lang.Throwable
at bib.aD(SourceFile:1745)
at bib.t(SourceFile:1665)
at bib.az(SourceFile:1000)
at bib.a(SourceFile:419)
at net.minecraft.client.main.Main.main(SourceFile:123)

A detailed walkthrough of the error, its code path and all known details is as follows:
---------------------------------------------------------------------------------------

– Head –
Thread: Client thread
Stacktrace:
at bib.aD(SourceFile:1745)

– Affected level –
Details:
Level name: MpServer
All players: 1 total; [bud['DiamondIoan_UK7'/2043765, l='MpServer', x=126.90, y=69.00, z=226.11]]
Chunk stats: MultiplayerChunkCache: 625, 625
Level seed: 0
Level generator: ID 04 - customized, ver 0. Features enabled: false
Level generator options:
Level spawn location: World: (24,64,256), Chunk: (at 8,4,0 in 1,16; contains blocks 16,0,256 to 31,255,271), Region: (0,0; contains chunks 0,0 to 31,31, blocks 0,0,0 to 511,255,511)
Level time: 155035 game time, 141712 day time
Level dimension: 0
Level storage version: 0x00000 - Unknown?
Level weather: Rain time: 0 (now: false), thunder time: 0 (now: false)
Level game mode: Game mode: creative (ID 1). Hardcore: false. Cheats: false
Forced entities: 67 total; [aam['Wolf'/2043678, l='MpServer', x=104.50, y=82.00, z=277.50], aam['Wolf'/2043677, l='MpServer', x=103.11, y=82.00, z=275.89], aam['Wolf'/2043676, l='MpServer', x=110.41, y=72.00, z=278.07], aam['Wolf'/2043675, l='MpServer', x=104.50, y=65.00, z=274.50], aam['Wolf'/2043674, l='MpServer', x=97.50, y=81.00, z=254.56], aam['Wolf'/2043673, l='MpServer', x=101.49, y=72.00, z=250.43], aam['Wolf'/2043672, l='MpServer', x=98.70, y=71.00, z=201.51], aam['Wolf'/2043671, l='MpServer', x=96.78, y=71.00, z=201.69], aam['Wolf'/2043670, l='MpServer', x=90.97, y=70.00, z=194.49], aam['Wolf'/2043669, l='MpServer', x=97.58, y=71.00, z=201.01], aam['Wolf'/2043668, l='MpServer', x=98.36, y=71.00, z=201.10], aam['Wolf'/2043667, l='MpServer', x=97.70, y=71.00, z=201.70], aag['Sheep'/2043666, l='MpServer', x=97.26, y=75.00, z=201.54], zt['Bat'/2043660, l='MpServer', x=80.50, y=54.81, z=260.34], aam['Wolf'/2043659, l='MpServer', x=81.70, y=51.00, z=261.70], aam['Wolf'/2043658, l='MpServer', x=80.86, y=51.00, z=261.11], aam['Wolf'/2043657, l='MpServer', x=88.51, y=78.00, z=238.28], aam['Wolf'/2043648, l='MpServer', x=78.48, y=59.00, z=260.56], aak['Iron Golem'/2043710, l='MpServer', x=133.34, y=117.94, z=173.69], aak['Iron Golem'/2043709, l='MpServer', x=136.97, y=118.00, z=174.13], aak['Iron Golem'/2043708, l='MpServer', x=139.03, y=81.00, z=178.11], aak['Iron Golem'/2043707, l='MpServer', x=134.29, y=117.94, z=172.02], ady['Villager'/2043706, l='MpServer', x=135.24, y=118.00, z=170.92], ady['Villager'/2043705, l='MpServer', x=135.87, y=118.00, z=170.92], ady['Villager'/2043704, l='MpServer', x=131.30, y=117.94, z=171.33], ady['Villager'/2043703, l='MpServer', x=134.51, y=118.00, z=170.92], ady['Villager'/2043702, l='MpServer', x=128.66, y=118.00, z=172.20], ady['Villager'/2043701, l='MpServer', x=129.00, y=118.00, z=171.30], ady['Villager'/2043700, l='MpServer', x=135.48, y=117.94, z=172.32], ady['Villager'/2043699, l='MpServer', x=129.72, y=118.00, z=171.30], ady['Villager'/2043698, l='MpServer', x=128.30, y=118.00, z=171.30], ady['Villager'/2043697, l='MpServer', x=127.66, y=118.00, z=171.30], ady['Villager'/2043696, l='MpServer', x=136.64, y=117.94, z=171.55], ady['Villager'/2043695, l='MpServer', x=136.53, y=118.00, z=170.92], aak['Iron Golem'/2043694, l='MpServer', x=131.95, y=117.94, z=172.44], ady['Villager'/2043693, l='MpServer', x=135.93, y=117.94, z=171.59], bud['DiamondIoan_UK7'/2043765, l='MpServer', x=126.90, y=69.00, z=226.11], ady['Villager'/2043692, l='MpServer', x=128.05, y=118.00, z=172.70], ady['Villager'/2043691, l='MpServer', x=132.05, y=118.00, z=171.22], ady['Villager'/2043690, l='MpServer', x=136.20, y=118.00, z=172.81], ady['Villager'/2043689, l='MpServer', x=129.35, y=118.00, z=172.20], aam['Wolf'/2043688, l='MpServer', x=129.50, y=63.00, z=168.30], zt['Bat'/2043686, l='MpServer', x=120.50, y=38.10, z=228.53], zt['Bat'/2043685, l='MpServer', x=122.75, y=38.10, z=222.25], ady['Villager'/2043684, l='MpServer', x=130.37, y=118.00, z=171.30], ady['Villager'/2043683, l='MpServer', x=127.07, y=118.00, z=172.30], ady['Villager'/2043682, l='MpServer', x=128.77, y=91.00, z=164.49], aam['Wolf'/2043736, l='MpServer', x=187.50, y=129.00, z=253.50], aam['Wolf'/2043735, l='MpServer', x=188.51, y=134.00, z=247.71], aam['Wolf'/2043734, l='MpServer', x=186.17, y=130.00, z=251.65], aam['Wolf'/2043733, l='MpServer', x=186.50, y=129.00, z=253.50], zt['Bat'/2044108, l='MpServer', x=186.98, y=15.23, z=176.48], zt['Bat'/2044107, l='MpServer', x=201.65, y=15.18, z=184.07], aam['Wolf'/2043719, l='MpServer', x=158.36, y=71.00, z=211.53], ady['Villager'/2043718, l='MpServer', x=156.56, y=89.00, z=191.95], ady['Villager'/2043717, l='MpServer', x=160.76, y=89.00, z=191.24], aam['Wolf'/2043716, l='MpServer', x=149.50, y=68.00, z=199.64], zw['Chicken'/2043713, l='MpServer', x=154.00, y=65.00, z=148.34], zw['Chicken'/2043712, l='MpServer', x=158.50, y=65.00, z=147.50], zt['Bat'/2043647, l='MpServer', x=92.36, y=71.50, z=194.01], aam['Wolf'/2043646, l='MpServer', x=73.58, y=64.00, z=148.50], aam['Wolf'/2043633, l='MpServer', x=52.72, y=123.00, z=252.51], aam['Wolf'/2043632, l='MpServer', x=52.28, y=64.00, z=244.57], aam['Wolf'/2043631, l='MpServer', x=52.04, y=61.00, z=242.70], aam['Wolf'/2043630, l='MpServer', x=55.61, y=61.00, z=240.90], aam['Wolf'/2043629, l='MpServer', x=55.00, y=49.00, z=224.02], zt['Bat'/2046307, l='MpServer', x=137.29, y=40.63, z=207.48]]
Retry entities: 0 total; []
Server brand: vanilla
Server type: Integrated singleplayer server
Stacktrace:
at bsb.a(SourceFile:366)
at bib.b(SourceFile:2587)
at bib.a(SourceFile:428)
at net.minecraft.client.main.Main.main(SourceFile:123)

– System Details –
Details:
Minecraft Version: 1.12.2
Operating System: Windows 8.1 (amd64) version 6.3
Java Version: 1.8.0_25, Oracle Corporation
Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
Memory: 343348280 bytes (327 MB) / 670441472 bytes (639 MB) up to 1060372480 bytes (1011 MB)
JVM Flags: 6 total; -XX:HeapDumpPath=MojangTricksIntelDriversForPerformance_javaw.exe_minecraft.exe.heapdump -Xmx1G -XX:+UseConcMarkSweepGC -XX:+CMSIncrementalMode -XX:-UseAdaptiveSizePolicy -Xmn128M
IntCache: cache: 0, tcache: 0, allocated: 13, tallocated: 95
Launched Version: 1.12.2
LWJGL: 2.9.4
OpenGL: AMD Radeon HD 7600G GL version 4.2.12422 Compatibility Profile Context 13.152.1.3000, ATI Technologies Inc.
GL Caps: Using GL 1.3 multitexturing.
Using GL 1.3 texture combiners.
Using framebuffer objects because OpenGL 3.0 is supported and separate blending is supported.
Shaders are available because OpenGL 2.1 is supported.
VBOs are available because OpenGL 1.5 is supported.

Using VBOs: Yes
Is Modded: Probably not. Jar signature remains and client brand is untouched.
Type: Client (map_client.txt)
Resource Packs:
Current Language: English (US)
Profiler Position: N/A (disabled)
CPU: 4x AMD A8-4555M APU with Radeon(tm) HD Graphics

Please note that your computer is below the minimum system requirements. So minecraft might not run as expected anyway.
But you may attach a short video demonstrating the issue, so we can look into it.

Sounds like a duplicate of MC-88632

Did you disable cheats when opening the world to LAN?
The "Cheats: false" in the crash report is not meaningful, see MC-8559.