Meshing of boundary layers wont work

I am trying to mesh (and, eventually, compute) a model of a rectangular duct connected to a circular hole, where the duct and the lower part of the hole are filled with water, the upper part of the hole is filled with air, initially. For better monitoring of the boundarys i am using the "boundary layer"-Function of comsol to increase the tightness of the mesh.

However the meshing stops with the error-message "Could not shift boundary node at all" which leaves me clueless because i dont know which boundary node could be meant or how to solve this issue.

Can anyone help me?