Solidworks 2016 has successfully stumped me yet again with its vague error messages. In this part, I'm getting an error when I attempt to perform an extruded cut along the length of the groove shown. I'm thinking that the complex, organic shape of the part may be the source of my troubles, but there isn't really anything I can do about that, in terms of changing the part. If you look to the very end of the feature tree, you'll see that I have a knitted surface which follows the curvature of the leftmost groove, and a sketch which I converted directly from the entities of the knitted surface.

I'm attempting to deepen the groove by 0.2" with the following procedure...

Sketch58 > Extruded Cut > Select Sketch Contour > FROM: 'offset surface' > Select Surface-Knit2 > Reverse Offset > 0.2"

The feature manager shows a pretty clean preview of exactly what I want, but when I try to execute the feature, I get the error message "Operation failed due to geometric condition"-- thanks solidworks, what an unhelpful and mystifying error alert.

I'm able to get the cut to work properly by building a spline along the groove that lies just barely within the edges, but this method produces a level of inacurracy that I'd like to avoid, not to mention it's fairly tedious and I have 5 more molds, similar to this one, that I need to make.

If someone could help me point out exactly where the geometry is failing within the groove, I'd be eternally grateful. Thanks!

NOTE: You can identify the geometry of the part infinitely easier if you go to View > Display > Tangent edges removed