Hi Robert,

Here are one or two pointers:

Make sure that all of the vertical curves touch the bottom ellipse exactly. Use your snaps.
Also, make sure that the bottom ellipse, ring shape, or whatever is precisely planar itself.
If none of those two requirements are met then the Network command may produce a surface with a non-planar bottom edge that may be just out of tolerance for a Join to the planar bottom surface.

Also, make sure, if you have made the bottom ring profile out of multiple curves, as I had done in the tutorial, that the ends of each touching curve are exactly tangent with each other.

However, if you are still unable to get the two surfaces to perfectly Join, consider doing the following:

Make a planar surface larger than the opening, and then move it up into the network surface with just a bit of the network passing completely through the plane.
Then select the bottom plane and the network surface and do a Boolean Merge. You should have four surfaces. Delete the excess and you should be able to join the newly trimmed plane and network surface together.

If for some reason, the edge curves are segmented, you should always first try to run the "Merge" text command, which is not the same as Boolean 'Merge'. The text command 'Merge' will often join the broken edge segments into one.

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....funny, I deleted your surfaces and re-made the network and planar again using your curves and everything worked. [???]
Must be a v2 vs v3 thing.
But still, take my above wisdom for what it is. :-)