Surfaces won't join - very frustrating and happens too often

 From:  Satoribomb
Hi Michael & MoI Community,

My apologies for grousing on Christmas eve, but I'm encountering consistent issues trying to create and join surfaces from networked curves. I've attached the 3dm file for reference. I'd really like to understand why I cannot join the red and blue surfaces, since they used the same curve at their adjoining ends for the network commands that created them. This is frustrating to say the least and not the first time I've encountered this kind of roadblock, just the first time I've been agitated enough to ask for help with it and not just give up.

Any help you can provide, once the Christmas holiday is behind us, would be appreciated.

Happy and restorative Christmas to you all