Have you managed to solve the entire Stage 5 Cipher Challenge? Solutions are now closed, but perhaps you want to take up the full challenge.

Patrick from Woodbridge School, England was the first to solve this cipher
Joseph from Hong Kong was the only other successful solver.

The solution is

Congratulations if you can read this, this encryption's getting quite complicated. The vigenere method of encryption commutes with a transposition if its row and column lengths are one more than a multiple of the keyword length, so in this case with a keyword of length two we need them to both be odd. I hope you've enjoyed decrypting these messages, why not try coming up with some ciphers yourself and testing your friends.

vigenere with keyword pi
transposition