Erik Kostson
Ansys Employee

The pipe288 as the name indicates is a pipe not a rod, so it is modeled as a pipe (section) not csolid which is only valid for a sectype,,beam (used for beam188).
So look in the help manual for pipe288 where it states (under cross section) that it can only be SECTYPE,,PIPE (this sectype does not have a subtype like a csolid which is only for a sectype,,beam, but this (sectype,,beam) can not be used as we said with pipe288, only sectype,,pipe can)

Finally if you want to see the difference between beam188 and pipe288, please see our help manual and under element reference and beam188 and pipe288.

All the best