How can I download a newer Yosemite installer? I have an existing Yosemite installer app from the original release of 10.10 (e.g. Install OS X Yosemite.app) but can't seem to download a newer installer.  When I click Download, I'm presented with this dialog:



However, clicking Continue doesn't appear to do anything.  No update appears to be in progress, no network activity shows in Activity Monitor.

The same dialog appears if I click the Download button in Purchases, and the download never begins.

How can I get an updated installer?
The problem appears to have been my copy of the installer that I had stashed away in a folder in my home directory, even though I'd originally made it by keeping a copy of the installer in /Applications (it was even owned by my user account instead of root!).

Once I removed that installer, the Mac App Store was happy to start the download for a new one.