[smt88]

Z is not a space, nor is N. That's all I've got for you, buddy. I can think of some code that would help, but I don't have time to write it.

Were you told that this is a traditional cipher, where characters are substituted 1:1?

Generally speaking, thinking really hard about this (and possibly failing) is going to be better for you than having someone on HN tell you the answer.