MrMarnic

Sorry your import was right. I was still on 1.16.5

What does the new error say?

And I believe the import should look like this: import net.minecraft.item.Item; without the world

In the run folder there is a logs and crash reports folder

And could you show your TestItem class please

Have you created a TestItem class?

Firstly you forgot the semicolon at the end of this line public static final RegistryObject<Item> TESTITEM = ITEMS.register("testitem", () -> new TestItem(new Item.Properties())) The second thing: In this line here: private static final DeferredRegister<Item> ITEMS = DeferredRegister.create(ForgeRegistries.ITEMS, MODID); You are using the variable MODID but you have never created it. You need to create it like this: public static final String MODID = "<your modid>"; Then it should work

Could you show your code please.

I will use the NTFS drive from now on

@LexManos and @diesieben07 I have found the real reason for the error message. It was the formatting of drive. Steps to reproduce (on Windows): Use a working drive/flash drive. Format it with NTFS => put the project folder on it => everything works fine Format it with ExFAT or FAT32 => put the project folder on it => I get the error message I have tested it out with a working usb stick. On NTFS => everything is working ON FAT32/ExFat =>I get the error I don't know why this is happening, but this seems to be the reason.

This could be, but in this post for example https://mcreator.net/forum/75274/build-and-launch-errors-need-help they say that they have the project on a flash drive and get same error. And when it is really failing, why does it work for any other version? Could it have something to do with the partitioning of the drive?

I am not using MCCreator. I just googled for the error message and found these posts. But it is just like this. If the project is on the E drive I get the error. If it is C drive it works.

I found the "solution" or better workaround. The runClient task works fine if the project directory is on the C drive. But on any other drive I am getting the error mentioned above. This only happens on 1.16.5, so there must be something that changed with the paths or something idk.

Not even that did fix it. But it seems like I am not the only one with this problem. Here is the same error https://mcreator.net/forum/73623/116-upgrade-not-working . And here: https://mcreator.net/forum/75274/build-and-launch-errors-need-help I really have no idea anymore. I just hope I won't get the error in 1.17 .

I don't have an answer either. I just tried out the 1.16.3 MDK and it works flawlessly. It's only the 1.16.5 version thats gives this error everytime, no matter how many times I reinstall it.