Invalidated Block Types

First it is important to understand that this is not an error, it is merely a notification.

There can be myriad of reasons a block cache is invalidate from updates to products, catalog price rule changes, and 3rd party extensions. Also running of cronjobs can cause block caches to become invalidated as well.

There are some community extensions available (listed below) that will refresh your blocks as the become invalidated.

https://github.com/tomasinchoo/Inchoo_InvalidatedBlockCacheFix

https://github.com/mklooss/Loewenstark_InvalidCache

This IS an error.

There is a CRON job problem (post 1.9.?) that runs and invalidates the HTML Cache, which produces problems (e.g. in my case, failed to carry over price discount to the Basket - so a customer would be charged wrong amount).

We shouldn't need to run an extension to fix a problem that has been introduced!