I tried downloading the new EpubCheck 0.3.8 plugin to replace my older version(0.3.7) on Sigil today. Unfortunately the new version failed to install and gave me this error:
Plugin plugin.xml is invalid or not supported on your operating system.
I then tried to re-install the older Epubcheck 0.3.7 version and that also failed to install with the same error.
One reason that might have something to do with this problem is the new version of Sigil 0.9.7 which KevinH released a day or so ago that I downloaded yesterday. Has the plugin.xml spec or handling been changed?
I've been running the new Sigil 0.9.7 version on Windows 8 for the last day or so.