It can be due to an invalidation or password change of your minecraft account.
To fix it, you just need to go into your %appdata%/.PixelmonEurope/launcher folder and delete the PixelmonEurope file.
Yes of course!
There is a "profile installer" on the launcher page that will install the last version of our mods + keep them updated under a profile called "PixelmonEurope" !
Yes you can ! The modpack will be also uploaded as a zip file.