My opponent cast [Ossification] on my [Absolute Virtue]. I had [Three Steps Ahead] in hand with available mana of appropriate color to cast the counter spell portion of the spell. That ability was grayed out, so I manually tapped [Restless Reef] and [Gloomlake Verge] for blue mana, then tapped [Riverpyre Verge] for one red to meet the mana requirement of 1UU on Three Steps Ahead, counter spell was still grayed out.

I have attached a screenshot taken shortly after my [Absolute Virtue] was exiled. There are no cards on the board, stack, or graveyard that prevent spells from being countered. (disregard that chose the draw a card and discard option on Three Steps, as I made that decision in frustration after I was unable to use the counter spell)

Except maybe [Absolute Virtue] interacting weirdly with [Ossification]? Like, maybe [Absolute Virtue] "this spell can't be countered" was somehow getting passed on to the [Ossification] targeting it?