Have you minted any Zerocoin? You need a minimum of 10 Zerocoin Veil in order to stake. You can mint Zerocoin by going to Settings icon > Zerocoin Minting.
Now I see. Thanks. I began minted process. Looks like it will take some time to get some zerocoin. Already pass 40 minutes and zerocoins still somewhere. I will wait and if get any problems will write here.