Version 0.4.3

Description: Exception in server tick loop

net.minecraftforge.fml.common.LoaderException: java.lang.NoClassDefFoundError: net/minecraft/client/util/ITooltipFlag
at net.minecraftforge.fml.common.AutomaticEventSubscriber.inject(AutomaticEventSubscriber.java:89)
at net.minecraftforge.fml.common.FMLModContainer.constructMod(FMLModContainer.java:599)
at sun.reflect.GeneratedMethodAccessor11.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at com.google.common.eventbus.Subscriber.invokeSubscriberMethod(Subscriber.java:91)
at com.google.common.eventbus.Subscriber$SynchronizedSubscriber.invokeSubscriberMethod(Subscriber.java:150)
at com.google.common.eventbus.Subscriber$1.run(Subscriber.java:76)
at com.google.common.util.concurrent.MoreExecutors$DirectExecutor.execute(MoreExecutors.java:399)
at com.google.common.eventbus.Subscriber.dispatchEvent(Subscriber.java:71)
at com.google.common.eventbus.Dispatcher$PerThreadQueuedDispatcher.dispatch(Dispatcher.java:116)
at com.google.common.eventbus.EventBus.post(EventBus.java:217)
at net.minecraftforge.fml.common.LoadController.sendEventToModContainer(LoadController.java:219)
at net.minecraftforge.fml.common.LoadController.propogateStateMessage(LoadController.java:197)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at com.google.common.eventbus.Subscriber.invokeSubscriberMethod(Subscriber.java:91)
at com.google.common.eventbus.Subscriber$SynchronizedSubscriber.invokeSubscriberMethod(Subscriber.java:150)
at com.google.common.eventbus.Subscriber$1.run(Subscriber.java:76)
at com.google.common.util.concurrent.MoreExecutors$DirectExecutor.execute(MoreExecutors.java:399)
at com.google.common.eventbus.Subscriber.dispatchEvent(Subscriber.java:71)
at com.google.common.eventbus.Dispatcher$PerThreadQueuedDispatcher.dispatch(Dispatcher.java:116)
at com.google.common.eventbus.EventBus.post(EventBus.java:217)
at net.minecraftforge.fml.common.LoadController.distributeStateMessage(LoadController.java:136)
at net.minecraftforge.fml.common.Loader.loadMods(Loader.java:593)
at net.minecraftforge.fml.server.FMLServerHandler.beginServerLoading(FMLServerHandler.java:98)
at net.minecraftforge.fml.common.FMLCommonHandler.onServerStart(FMLCommonHandler.java:333)
at net.minecraft.server.dedicated.DedicatedServer.func_71197_b(DedicatedServer.java:125)
at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:486)
at java.lang.Thread.run(Thread.java:745)
Caused by: java.lang.NoClassDefFoundError: net/minecraft/client/util/ITooltipFlag
at java.lang.Class.getDeclaredConstructors0(Native Method)
at java.lang.Class.privateGetDeclaredConstructors(Class.java:2671)
at java.lang.Class.getConstructor0(Class.java:3075)
at java.lang.Class.getConstructor(Class.java:1825)
at net.minecraftforge.fml.common.eventhandler.EventBus.register(EventBus.java:128)
at net.minecraftforge.fml.common.eventhandler.EventBus.register(EventBus.java:112)
at net.minecraftforge.fml.common.AutomaticEventSubscriber.inject(AutomaticEventSubscriber.java:82)
... 31 more
Caused by: java.lang.ClassNotFoundException: net.minecraft.client.util.ITooltipFlag
at net.minecraft.launchwrapper.LaunchClassLoader.findClass(LaunchClassLoader.java:191)
at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
... 38 more
Caused by: java.lang.NullPointerException

I bet I forgot a sided check in the tooltip event.

If you're willing to test, its attached. I had not tested separate client and server before and I found a bunch of other junk to fix for seals, but it doesn't crash anymore and tooltips work.
ThaumicComputers-MC1.12.2-0.4.4-beta.1.jar.zip

Fixed in 0.4.4

If you're willing to test, its attached. I had not tested separate client and server before and I found a bunch of other junk to fix for seals, but it doesn't crash anymore and tooltips work.
ThaumicComputers-MC1.12.2-0.4.4-beta.1.jar.zip

Sorry I missed this - I'm always willing to test.

I've downloaded the latest.