Okay, no problem bloom.

But a question:
Do you play on PC or Xbox?
I play on xbox ... and If I'm right, as your hero see the icon "ladder", push A on the gamepad and than walk forwards (using the stick for going forwards);
If you stop using the stick fro going forwards, you stop climbing and hanging on the ladder ...
It can be you fall from the ladder if you accidentally using the stick sideways, that's possible.
So, keep the button until you're up. Your hero will go automatically to the next platform (then stop using the button) with a sideways jump (men) or a nice twist (female).
Sorry if I'm not so clearly .. but I climb now all ladders in Divinity II without thinking about HOW to climb them .. I do it automatically, like I bike or riding in a car.
Success!