What could cause a sudden increase in pages "blocked from robots"?

Selected answers from the Dumb SEO Questions Facebook & G+ community.

• 
  Pablo Caño: Hi everyone!
  
  Question for you all:
  What would be the reason to sudden increase in pages "blocked from robots"?, according Google Webmaster Tools. I didn't touch the robots file for a long time.
  
  Curious to hear your thoughts! ;)
• 
  Federico Sasso: An increase in links pointing to robots.txt blocked resources, previously unknown to Google?
• 
  Ritu Ahuja: I would like to know the answer too. I have never heard this before.
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  Rob Maas: Curious to see the robots.txt
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  Federico Sasso: Curious also to know whether the robots.txt is always reachable by googlebot
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  Daniel Kamen: Have you changed the file name structure recently? If you are on a CMS, changing some setting unknowingly then this might have changed the file name. Can you share more details? ;
• 
  Pavel Joser Atauchi Rojas: Generalmente esto sucede cuando utilizas una plantilla en un CMS, como menciona #Daniel  ;ha podido estar bloqueando la indexación.
• 
  Rahul Chauhan: there can be various reason for this which can only be solved if some more details are provided with.
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  Edwin Jonk: From the expert panel in this weeks SEO Questions hangout on air on 00:21:09 into the YouTube video: https://dumbseoquestions.com/q/what_could_cause_a_sudden_increase_in_pages_quotblocked_from_robotsquot +Pablo Caño
  
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