Hello Pablo,
the operation Verticallist.SelectedItem++ is the correct approach to adapt the selection within the vertical list. Triggering the operation from the 'outside' of the GUI application should also work. In your question, however, you mention a memory error. I assume, you get a CPU exception.
Question 1: Is your application using multiple threads?
Question 2: Is the code containing Verticallist.SelectedItem++ called from an external thread?
Please note: the entire GUI related code may be called only in context of the GUI thread. No other thread may call the Embedded Wizard functionality. See also: Take care in multi-threading environments.
Question 3: How does the 'outside' code call the Embedded Wizard code?
Question 4: Do you have a debugger in the target system? If yes, can you provide more details concerning the location where the exception occured?
Best regards
Paul Banach