I have verified that you are indeed a registered user, however the FlashFXP ID you entered is invalid.
This leads me to believe that the copy of FlashFXP you are using has been modified or tampered. There are many websites offering FlashFXP for download and it's often easy to mistake it as an authentic release.
I would recommend you download FlashFXP directly from our website at
https://oss.azurewebsites.net/download.php
This should also resolve the problem you encountered. besure to update your profile with the new FlashFXP ID