I have read that Google is currently making changes to the store for Chrome about how add-ons are handled. I can't say what the changes actually are and if they would affect this since the particular article I read was rather vague on that issue. Something about disabling certain apps from loading from 3rd party links, and that many would now have to visit the store in order to obtain add-ons, etc. If you're trying to download the Ad Blocker from the publisher website, then search the store for Chrome and locate the Ad Blocker there for download.
My advice is to make sure you have updated Chrome to the latest version before proceeding.
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