@Arian Trayen
I think you have manually given the version number while registering the HDP version just by giving version number. You have provide the HDP-2.6.4.0-91.xml file which will have correct version files in xml with resective to that HDP version.
Step-1 : Just follow registration process as is, but when you HDP 2.6, just click drop down, there you can see 'Add version', click on it as shown in screenshot.

Step-2: Now either upload the version file by downloading the HDP-2.6.4.0-91.xml file from local repo/public repo else provide the URL clicking second option provide either public or local repo referring to that xml.

hdp-2640-91.xml
For you I have attached the HDP-2.6.4.0-91.xml file and even you can use public repo
http://public-repo-1.hortonworks.com/HDP/centos6/2.x/updates/2.6.4.0/HDP-2.6.4.0-91.xml.
Hope this helps you.