Hi guys,i'm having problems doing a Cut-Extrude feature in an assembly (See attached).

What I'm trying to achieve is basically a rectangular cut, using a sketch drawn on the base of the support strips, then cut-extruding it up to a curved surface (the ellipse in green). As there wasn't an 'Up to surface' option available under 'Direction 1', I had to do it the other way round; project my sketch onto the curved surface then cut extrude it down by a specified distance.

Why isn't this 'Up to surface' option available or can it not be done in assemblies?

Anyways, this method allows me to do those cuts but I'm now having trouble doing a cut extrude for the rest of my sketches (without the yellow preview), within the ellipse boundary even though I try the same steps..I keep getting this error message:

'The projection of the sketch on the surface failed. Please check that the sketch is completely within the surface/plane/face & that it is projected onto only one face.''

Any input would be greatly appreciated.