CB / Casus Belli

[bindie]

I have encoutnered a small problem as leader of the Greyjoys during the Blackfyre Rebllion time period. One of my vassals did not respond to the call to arms and declared themselves independent. The War has been won (by the Blackfyres again) but Volmark will not come back under the Highlordship of the Iron Islands. I have tried to declare war on Volmark since they would not accept my offer of vassalisation, however it would not let me declare war due to there being no Casus Belli, which is odd because Volmark is one of the islands apart of the Highlordship of the Iron Islands. So what is wrong here and why wont a CB register?

Any help is much much appreciated.

 

[Rifal]

If Volamrk is Duchy tier:
console: give_title d_volmark <your characters ID>
If Volmark is County tier:give_title c_volmark <your characters ID >

To find your Characters ID
Console: charinfo