This is super frustrating. We keep getting errors when we try to upload the code.
We've just published v1.0.15 of the Create Chrome app to address this.
You can visit chrome://extensions (http://chrome://extensions) to check which version you are at, there's an update button on that page to manually update, if that doesn't work you can also try to reboot the Chrome OS device.
Please let us know if you have any further issues.