This item and all items under it will not be crawled because the owner has set the NoCrawl flag to prevent it from being searchable

​This error may appear in the crawl log when you are trying to crawl SharePoint sites. This is particularly likely for the MySites host because this template has the flag set to NoCrawl by default.

To solve the problem go to your MySites host (or other problem site collection) and go to Site Settings. Under Site Administration go to Search and Offline Availability. Set the flag to "Allow this site to appear in search results".