I just bought some Gridcoin (GRC) on Poloniex and tried to send them to my wallet, but Polo says "invalid address".

Am I missing something here?
I got the Gridcoin Wallet "3.1.8.5-research". The addresses always start with "S" but the ones on Polo start with different letters. Whats wrong?
Should I use the "classic" wallet?

Completely confused...