No Insert = TRUE and No Update = FALSE on the Opportunity business component.

No Insert = TRUE and No Update = FALSE on one of the fields of the Opportunity business component which is displayed in the list applet but not in the form applet.

No Insert = TRUE and No Update = FALSE on the Opportunity List Applet.

No Insert = TRUE and No Update = FALSE on one of the list columns of the Opportunity List Applet.

You failed to compile the Opportunity List Applet, hence it is still checked out and cannot accept new data.

Your responsibility is not correctly configured; you do not have permission to see the New Opportunity view.