DNS error on webmaster tool

[tpt.com]

Google webmaster tool is showing DNS error and that is leading to many server error (502,500) almost 50+ in every crawl. Recently Google crawled one of our sub domains that we did not want google to crawl. We blocked it via Robots.txt and also removed all the URL's and since then we are having this issue. Any suggestions how to fix this DNS error? Thanks in advance.

[sangodep]

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