Fuming

So whats your game we buy 4.0 last year and bang next time its 5.0 and now I can't use it any more? is this your game, we buy it you upgrade, we have to buy again simply furious and I will be telling everyone not to buy your upgrades because its an utter waste of money!
If I have a 4.0 edition I should be able to use all filters from 2.0 to 4.0 that makes sense right?
No in your illogical world of lets rip off our customers you block the one I bought well thank you very much I most certainly won't trust you again until you unblock it and I am not a fool I won't be upgrading to 5.0 when 6.0 is already on the market.
Shame on you.

Carl is right, You do not need to buy the upgrade, just click on the ok to download free the latest version

See these threads

FF 4 upgrade

And

Avoid confusion