Moving to different weeks in the portal timesheet

Hi

We are operating Web Dynpro ABAPESS timesheet.  We are currently going through the patching process and have encountered a problem.  When using the timesheet it is no longer possible to move to different weeks.  Below are the settings we have for the timesheet entry profile in the Time settings part.

Period type                2   Weekly data entry                                                     Periods               1

First day of week      Monday

Start date relative     Blank    Lower limit relative     Blank     Upper limit relative         Blank

I have tested and entering 99 in the Lower limit relative will allow us to go back to April 2012 but at the moment in our productive system will can go back to 2005 (our go live).   If I enter 4 in the periods field I am allowed to go back to July 2006.  Ideally I would like user to be able to go
back to our go live.

I have two questions:

1)            Why when leaving the “Lower limit relative” blank allowed users to move to whatever week they wanted to, does not work any longer?

2)            What is the connection between period field and the lower limit relative field?

Thanks

Mark