I recently upgraded my subscription. I have been unable to successfully install any of the upfront child themes. I have twice removed the upfront and child theme directories and attempted to reinstall. I always get the error button, but no error information is available.
The strange thing is that the themes page, both yours and the standard wordpress themes, think they are installed (until I remove the directories). When I attempt to preview the themes, it goes back to the themes page and I have to shut down the page to do anything.
I am using WordPressMU and sub-domains.
Thanks for your help,