Smoothing makes a mess of faces

[changrilla]

Hi. I'm hoping there's a solution to this. I want to smooth the edge contours of a guitar body but it makes a bit of a mess of the faces. 

Edges selected: https://mgcsoft.com/Wings/EdgeFacesSelected.jpg

After smoothing: https://mgcsoft.com/Wings/EdgeFacesSmoothed.jpg

Any way of avoiding the unwanted edges. Cheers, Gordon