Using Windows 10 1703 Build 15063.540
I've not fired up FlashFXP for a little while, so went to check if I am on the latest version.
I've had it confirmed from another forum member that they have had this problem too (although I didn't confirm OS version).
Checking Help->Check Version the following happens :
3 radio buttons each flash green, and then very quickly it reports the following in the dialogue box :
Error:Not Found
https://oss.azurewebsites.net/download
In the mean time a web page is loaded in a default browser and returns that I am on the latest version.
Cheers