"GO" button greyed out for certain bosses

[Inculpatus]

I can do Barlog and Zakum just fine, but Ursus and Magnus are grayed out for me, I mean I can click on them and all, but I can't click "GO", it says I need to check and meet the requirements but I'm level 137... why can't I boss them?

 

[Donut]

I can do Barlog and Zakum just fine, but Ursus and Magnus are grayed out for me, I mean I can click on them and all, but I can't click "GO", it says I need to check and meet the requirements but I'm level 137... why can't I boss them?

Please see the boss prequest guide.