Decipher Minecraft Server Crash Report?

I have created a server with modpack over Nitrado. This runs well until you place a block. Then he crashes and gives the message "server closed". It also creates a crash report from which I will not be smart.

Here is a link to the crash report:

Maybe you do not have enough ram

It is not on the server. This runs long and fluid until you place a block. And the maximum load is 80%.

The error message is pretty clear: the class

net.minecraft.client.Minecraft could not be found.

Whatever - i.e. At server start, the necessary jar file was not specified or entered incorrectly.

But I'm not a Minecraft but a Java specialist…

Schaumal in the crash report from line 111, there's reported by the error.
In my opinion, it is the MOD (Buildcraft.jar) that causes the error.