My NAS which showed fine in Finder on Yosemite, just does not after the 'upgrade'. Also repeated Time Machine errors as below. Never had these issues on Yosemite. The NAS is a WD MyCloud. Lots of others with the same issues too. http://community.wd.com/t5/My-Cloud/Support-os-x-el-capitan/td-p/906456 The Time Machine error comes every 24 hours or so, and it starts afresh.