When I press the Get button it states "Invalid From date specified". How do I stop this?
Firstly, make sure your Period From and Period To dates are within the range that HMRC permit. 1 year plus 1 day in the past from the current date is the furthest back, and the current date is the furthest forward.
Secondly, make sure your Windows date is set to United Kingdom (dd/mm/yyyy or dd/mm/yy). An American date is not permitted!