Go to your relational graph and open the relationship between your main layout and that portal. Be sure that 'allow creation of related' is checked on the child (portal) side. The relationship must be based upon a standard field in the child table which matches = the same field in the parent side (ie, parent:: pk_parentID = Portal:: fk_parentID. When 'allow creation' is checked, typing into a field in the portal will create a new portal record and insert the parentID into in portal's fk_parentID field.
I am having the same problem and we have done all of the above in your answer. What aren't we getting??? The relationships are correct in our portals. I don't know what is wrong with these second line not working. The first line will work but once you add a second line, it just changes the top line to whatever you selected for the second line and you ant continue on the second line.
Please post a detailed description of the relationship that defines your portal.
Make sure that the fields you placed in your portal refer to the same table occurrence as your portal or a Table occurrence that is related to it.
Make sure your layout refers to a table occurrence that is related to the table occurrence you've specified for your portal.
(Table occurrences are the boxes located in your relationship graph)