We would need to know more about your database design before we could answer your questions.
A table occurrence name is specified for your layout in Layout Setup... | Show Records From. Another table occurrence name is specified for your portal in Portal Setup.... Show Related Records From. These are the names of "boxes" found in Manage | Database | Relationships.
What is the relationship between them? What are the match fields you have specified?
Is there any portal filter defined in portal setup for your portal?