System.NullReferenceException:

[SteliosLL]

This is where i get the exception.

With most schematic files it works ok. But with some other schematic files i get this error "System.NullReferenceException"

[mstefarov]

You are most likely getting a NullReferenceException because root.Get(...) cannot find a tag named "Blocks". When a given tag cannot be found, root.Get(...) returns null. Trying to get ByteArrayValue from that null will throw a NullReferenceException.

Could you share an example .schematic file please? It's possible that the capitalization is wrong ("blocks" or "BLOCKS" is not the same as "Blocks") or that the tag is missing.