Casting "greyed" out spells

[Shmonk]

Question - in an SP game I had my Pretender enter the water to take a water province, and I thought I scripted him to cast Water Shield and 1 or 2 other buffs before going to attack closest. Now when the turn started, he cast no spells, just ran over and died after taking on 25+ ichtyids.

Now I thought if I had the ability to select a greyed out spell like Water Shield (I was on land at the time), it would still work as I moved to attack a water province. Is this not true?

It's possible I canceled the scripted orders somehow, but wanted to know in general if this was the case.