Another thing I forgot to mention, since this was a problem that a lot of students here forgot to do first before modeling in Houdini.

In SOP, make sure that you turn off your the Secure Selection (I call it a.k.a “selection lock”) The selection lock is located on the left side of the bar where you'll find the lock icon. The default is on. You can turn this off by default by going to the Preference>Tools>“Sop-Level Secure Selection On by Default”