Companion bug cant activate them

If you are a Smith of Kitava you cannot spawn a companion with Heat of the Forge or Manifest Weapon

I should have enough Spirit - cant click it.
Bugged!

If any of you are playing a Witch & an Infernalist, make sure you don't have the Infernal Hellhound active because it counts as a companion. That was the issue for me.

I had the same issue, got a Nettle ant with companion. It said 24.9% spirit, but in reality it took 175 spirit, not sure how the calculations work behind the scene.
To solve it, I just unsummoned all my minions to open all spirit and then activate it. Yes, the tool tip doesn't properly display the reservation cost of the tamed companion. Hope it helps

I had exactly the same issue and root cause of it was a wand that grants Spellsinger skill. It didn't allow me to activcate companion until I inserted a random skill gem into Spellsinger slot. Without this wand or with another wand that grants different skill companion is activated without issues.

Hope this may help others.

In 0.3, I had this issue. When equipped with Svalin unique shield, the companion does not shows up. Desequip and equip the shield back, and it seems to fix the bug