I am new to OpenERP. When I click POS and click on start "New Session". it gives me an error message:

Error! There is no period defined for this date: 2013-06-18. Please create one.

I have checked in Financial Accounting Section (Under Configuration) there is a monthly period open for each month of 2013. I also created a new period for this specific date but still no success. I get the same error message. Can anyone help please ?