$ dig nedgros.de any
...
;; QUESTION SECTION:
;nedgros.de. IN ANY
;; ANSWER SECTION:
nedgros.de. 86301 IN CNAME nedgros.herokuapp.com.
Short answer: you cannot have a CNAME at the "top" of the zone, a CNAME is an alias or reference, it cannot coexist with any other data. Specifically, it cannot coexist with a NS and SOA records which are rather important for the correct operation of your domain. RFC 1912 Section 2.4.
You have not properly followed the Heroku instructions. See https://devcenter.heroku.com/articles/custom-domains , if this setup is what you want read the part on "Apex domains".
You can add other records as required, there are still constraints on valid data, you should use one of the web-based tools to check www.dnscheck.com is straightforward (and captcha free).
– mr.spuratic Jan 15 '13 at 10:43