possible duplicate with #2562
I know it's only a stacktrace and no major problem, but here's what I was told to report anywys:

[18:30:32] [Server thread/ERROR] [immersiveengineering]: Compat module for tconstruct could not be preInitialized. Report this and include the error message below! slimeknights.tconstruct.library.TinkerAPIException: [TCon API] Could not register Material "constantan": It was already registered by Moar Tinkers at slimeknights.tconstruct.library.TinkerRegistry.error(TinkerRegistry.java:951) ~[TinkerRegistry.class:?] at slimeknights.tconstruct.library.TinkerRegistry.addMaterial(TinkerRegistry.java:129) ~[TinkerRegistry.class:?] at slimeknights.tconstruct.library.MaterialIntegration.preInit(MaterialIntegration.java:101) ~[MaterialIntegration.class:?] at blusunrize.immersiveengineering.common.util.compat.TConstructHelper.preInit(TConstructHelper.java:92) ~[TConstructHelper.class:?] at blusunrize.immersiveengineering.common.util.compat.IECompatModule.doModulesPreInit(IECompatModule.java:94) [IECompatModule.class:?] at blusunrize.immersiveengineering.ImmersiveEngineering.preInit(ImmersiveEngineering.java:93) [ImmersiveEngineering.class:?] at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[?:1.8.0_202]

Moar Tinkers' Constantan conflicts with the one of immersive engineering. That's all.

alright, you have two choices, disable Constantan and Treated Wood in Moar Tinkers, or disable the TiCon Integration module in IE

That's not really true and a pretty dumb statement from Alex, actually =P

The proper solution is that I start catching that error rather than letting it propagate.
The reason I currently don't is that no other mod added Constantan until IE did.