Thank you all the replies.
The windows where from a library I have for a while.
They come in with 2d Planes and I shell and copy them , and generally use the mirror glass and turn down the opacity in the setting to 0.25.
I rebuilt the glass, and re applied the material and it seems fine now.
So
" NEVER TRUST AN IMPORTED MODEL"
My golden rule generally ,but sometime your tied for time.
Thank you all for the help, and yes it was the normals I would say.
Philip