I'm Ireland and I'm allies with the Lombards. They've following me into a few wars I've in Scotland, and I've followed them into a few. But when I'm declaring war against France for a claim on Nantes the Lombards are not listed amongst the allies that will join the war and after declaring war, the "call to arms" diplomacy option with the Lombard screen is greyed out because with an x next "we are in a war we call [king of the lombards] into" (or something like that, I can't remember the exact wording). My searching for reasons why allies won't join a shows one ally being a vassal or one ally having a non-aggression pact with the defender as common reasons to prevent a call to arms. We're both independent and neither of us have a non-aggression pact with the French. So does anyone know what else might be stopping the call to arms?