Error 306 when click Start local harvesting

Hi I get Error 306 when I click the button Start Local Harvesting. I just created wallet - it is still synchronizing. Do I have to wait for sync to be done? Is that the issue? What else could be the issue? I have Windows 64 and Java Installed and I used the Windows Installer. Everything seems fine - it says synchronizing except I get Errror 306 when try to click Start Local Harvesting.

Do you have 10,000+ VESTED XEM?

Are you sure the node has available harbesting slots?