Transaction code created. Can't run it from command t/a line but can by Transaction->Execute. Why?

Question

Why can't I run the program typing the transaction code created for the program here:

but I can using Chosen Transaction->Execute->Direct Processing?

Answer 1

Type in /nZOOO_MAINPRGM if you would like to run the transaction in the existing session, or /oZOOO_MAINPRGM if you would like to open a new session.

Given that you say you can execute the transaction from the workbench, this should work. If it does, you should also be able to run your transaction using ZOOO_MAINPRGM, provided you are in the SAP main screen and not within another SAP transaction.