I'm so sorry, I thought I attatched the f3d file.
Two holes, one 22cm, one 18cm, reduction in size for an increase in velocity. I thought I would use a loft to create the slow decreease in pipe size from 22cm to 18cm. However, when I created the guide rail, so that the pipe would curve downwards I get that error. I've made a silly mistake while sketching the guide rail and I just don't understand where it is.
This is just a concept design to experiement with fluids, all that's gone wrong is me forgetting the principles of using guide rails with a loft.