Troubles by Lighting build with transparent objects

[Mathisxy]

Hi there,
My Problem is, that I try to build my lighting with stationary lights in a “tunnel”. To create the tunnel I had to vertex paint parts of stones and cliffs, that are around the tunnel, transparent. I set the opacity to masked.

With movable light there are no problems, but if i bake the lighting (stationary lights) there are those artefacts as seen on the pictures below:

My question: How can I perevent those artefacts? Are there some transparent lighting bias that I have to increase?
Thanks for youre answer!

[Mathisxy]

I tried a few more things and know I think the problem is clear:

The Transparent material still casts shadows, when it is baked. So i want that material to cast NO SHADOW where it is TRANSLUCENT. I think with a masked material that should be possible, because Alpha is wether 1 or 0:
Maybe its causes problems, because i vertex painted the opacity…