Originally Posted by findark

The computer is broken and will not recognize Z as a valid booking class for the cert (valid classes per computer are A and I). It takes a few HUCA to find an agent who understands the problem, and that the computer is wrong, and to issue an override.

There may exist another computer which will complain if the I fare requires Q or K space; I have a vague memory of this being an issue once, but the problem with Z is the main issue right now.