Thank you very much, Hasan. I was adopting the wrong approach in implementing a Accounting Calendar with an Adjusting Period.

You have set me right, and this is how I can put it for other Forum Users:

Answer2: The correct approach to adopt when creating a calendar with adjusting Period.

A calendar must contain all periods of same "type".

Assuming only one adjusting period for Year 2009:

This is what you should do:
1) Create a new Type as:
Period Type: "Month13".
Period per Year: 13.
2) Create a new calendar based on this type.
3) Create adjusting period as ADJ (Prefix name) with Period Type of Month13
4) Year is the same
5) Quarter is 4
6) Number of Period is 13
From: 31-Dec-2009
To: 31-Dec-2009
Name: ADJ-09
Set Flag to Yes (Tick)

When the periods within the calendar is running out, we have to append extra periods to this calendar in question (one full year periods should be added). However, you can add few months as well (but Budgeting will not work, if you implement budgeting).