There seems an issue on the zerocoin tab, mintzerocoin button. It does not work. The mintzerocoin function works as I can do it in the Console window by typing the command directly. But "mintzerocoin" button always give me error. And with more testing, it seems that "mintzerocoin" button actually does the "spendzerocoin" function. Dev please check and fix.
Thanks for reporting the issue. Somehow one function call is messed up. I fixed the issue now and updated the github. For those who want to mint zerocoin, please use the Console Window to do so. At console window, just type "mintzerocoin amount". To spend zerocoin you can use UI or command line to do it, both will work. Updated windows/mac wallet will be provided later. Not mandatory for upgrade.