missing base game...weird its an expansion for race 07 that i already have...try to create support ticket and ask about this issue...

There's a bug with Race On giveaways and nobody can enter...
http://www.steamgifts.com/discussion/4sZZR/bug-impossible-to-enter-race-on-giveaways

Your key/gift is Race On expansion pack or Race On Bundle?

• RACE On - Expansion Pack for RACE 07: https://steamdb.info/sub/2278/apps/ (Only RACE On - Expansion Pack Content)
• RACE On Bundle: https://steamdb.info/sub/2277/apps/ (Race 07 Base Game+STCC: The Game+RACE 07 - Formula RaceRoom Add-On+RACE On - Expansion Pack Content)

If this is from the bundle, you could create a giveaway for "STCC - The Game" instead :)