When a user opens case entry and creates a new case record I would like to set the value of the Full text textbox with a list of questions for users to ask when on a call.
Your pre-processing on get new won’t have a row to update yet. You can try on post-processing, or you may have to put it on update. Run a trace where you open a new case and the first thing you do is put some text in that box. See what the last method called is.
Pre vs Post is the issue here. You need to pay attention to what the method is doing. Typically, we use Pre when we are saving because we want stuff to happen BEFORE a save. In this case you want to set a value on a new row. If you use Pre, the record does not exist yet because the method didn’t create it yet. You will want to use Post for this one (and almost all GetNew methods).