There are a few questions about coins.
I sent 1 zerocoin and then I was sent 1 zerocoin. Now I have 10 ringST, how to mint them in zerocoins?
Can I mint back a zerocoin to basecoin?
You can manually mint Zerocoin by going to Settings> Zerocoin Minting.
In case that doesn't work you can convert RingCT to Basecoin through the console, which can then be minted in Zerocoin Minting (check the checkbox for Use Basecoin):
sendringcttobasecoin BASECOINADDRESS AMOUNT