The App Center Builder is working without issue.
What is your Cordova version setting. See Window>Settings>App Center to find this setting.
Set it to Cordova 2.9.1 if it is set to anything other value. Then try building.
Lastly, create a new project with the default design and attempt to build it. Does it succeed or fail in a similar manner as your currrent issue. If it fails then I suspect the issue is on your side with either antivirus software, firewall, … let us know how the results of the test above.