Texturing problem with polygon selection.

Hello.

i want to apply a graffiti on a brick wall in c4d. i have a ploygon selection with the brick wall texture and use parts of the same selection for

the graffiti texture. the alpha map for the graffiti is fine and works on other objects. when i apply the texture on the selection the brick wall is covered

by a white field…can some one tell me what is the problem here?

thanks in advance.