Druid problem at Sanctum of the Serpent God, Part 4, Ydersius

[playerx]

Hello everybody
currently we are playing part 4, Rise of Yderius.
We have our army, and actived the "descent" and are now heading for the sanctum. Our level is 15-16

But suddenly all of our casters have to roll at every (!) spell a check against their casting class difficulty 30! As i am only lvl 15 I must beat 15 at every cast or the spell is lost.

Is this written in the book? I am just asking as your GM hates magic-user and we cannot believe how to fight with 75% of all our spells failing?

I need some advice as currently all our magic-user are going to hate the end of this interesting adventure path!

Maybe our GM is just misreading some rules? Otherwise can you confirm this by telling us page no. etc.?

[NobodysHome]

While I normally frown on replying to players asking about the way their GMs run the game, in this case it may well be a simple misunderstanding on your GM's part.

On p.34 of the book, the text reads, "...forces anyone attempting to cast a spell...to make a DC 30 Concentration check or lose the spell..."

So it's not a caster level check, it's a Concentration check, and you get to add your ability bonus and any feats (for example, Uncanny Concentration), making it more than likely that your spells have a greater than 50% chance of working.