I've turned to my rarely-used PC version, which was showing 'licence expired' under the flightplan section (which it's not, it's valid to May 2015). Deleted the programme (which was out of date anyway) and downloaded and installed the latest version. It still shows 'licence 'expired'. Everything works fine on the iPad, however. Any ideas?

On trying to load charts, I was told that I couldn't because I was logged in elsewhere. Closed my iPad verson down and this fixed both problems. 

If your copy of SkyDemon thinks your subscription has expired, the solution will always be to log out (from the Setup menu) then log back in again. Recent versions of SkyDemon do this for you transparently behind the scenes, but if you were using an old version, you might find it necessary.