Originally Posted by GreyWolf
there's not enough tenebrium. The funny thing is, I have got 30 bars in my inventory.

The message is referring to Tenebrium the skill, rather than the bar; level 3 is required to combine tenebrium bars with a weapon.

Originally Posted by Georgiy Savchuk
I have a few more questions:

3. Yes, the skill preview is not exact and the effect can hit or miss characters near the edges not indicated by the preview, depending on the terrain and skill.

4. I guess not based on your description. Divine Light sets the Warm status, and Burning is listed in Bodybuilding's tooltip, so apparently lesser variations are not included (Chilled isn't listed, but Frozen is). Based on the listed statuses, it should be possible to determine whether skill effects would be blocked by Bodybuilding or Willpower.
Speaking of Divine light, though, IMO a more significant omission that skill's tooltip not mentioning that it removes surfaces and clouds in its cone of effect.