Why can't I declare war to press my own claims?

I'm trying to devour the Byzantine Empire piece-by-piece. But despite owning the Kingdom of Thessalonika, I am absolutely unable to press my Bishop's... "legitimate" claims against the Basilius!

Ionia is rightfully mine, darn it!

What gives? Why am I unable to press my claims?

Is your male ruler, perhaps, in the Learning lifestyle?

In 1.1, you cannot press "Your Claims" while celibate -- a strange oversight that does not seem intended. A reasonable assumption is that the ability to press your own claims is intricately tied to the ability to father children -- Eunuchs cannot inherit titles for instance -- and the game thinks you're ineligible as long as you're celibate.

As a work around, simply "Renounce Celibacy", begin your wars, then "Embrace Celibacy" once more.