Thx you very very very very very much. In my case, it was an issue with my Facebook Account which cannot sync contacts because of a wrong password..
"
21/10/2015 00:45:50,578 AddressBookSourceSync[3069]: [CardDAVPlugin-ERROR] -getPrincipalInfo:[_controller supportsRequestCompressionAtURL:https://originalprankster_33%40hotmail.com@webdav.facebook.com/576986402///originalprankster_33%40hotmail.com@webdav.facebook.com/576986402/] Error Domain=CoreDAVHTTPStatusErrorDomain Code=401 "(null)" UserInfo={CoreDAVHTTPHeaders=<CFBasicHash 0x7f8d54e98d70 [0x7fff7c339390]>{type = immutable dict, count = 11,
entries =>
0 : x-fb-rev = 1997856
1 : Content-Type = <CFString 0x7f8d549e3cf0 [0x7fff7c339390]>{contents = "text/plain; ; charset="utf-8""}
2 : x-fb-trace-id = <CFString 0x7f8d54912230 [0x7fff7c339390]>{contents = "FJdsxuNkWGb"}
3 : Pragma = no-cache
4 : Expires = <CFString 0x7f8d53798330 [0x7fff7c339390]>{contents = "Sat, 01 Jan 2000 00:00:00 GMT"}
6 : Date = <CFString 0x7f8d537ed8d0 [0x7fff7c339390]>{contents = "Tue, 20 Oct 2015 22:45:50 GMT"}
8 : x-fb-debug = <CFString 0x7f8d549db560 [0x7fff7c339390]>{contents = "hXt0KQJW2eJOqDL6U7HjJihXnoKg/+mCFyHZxWuxI1JWER550PxMjMnCTdhltJwtWuAXZ7/TVJzKDN Xz5O1fTg=="}
9 : x-fb-stats-contexts = <CFString 0x7f8d54ea8490 [0x7fff7c339390]>{contents = ": api, : V3"}
10 : Www-Authenticate = <CFString 0x7f8d54e73250 [0x7fff7c339390]>{contents = "OAuth realm="Facebook WebDAV", Basic realm="Facebook WebDAV""}
11 : Content-Length = 40
12 : Cache-Control = <CFString 0x7f8d549d3720 [0x7fff7c339390]>{contents = "private, no-cache, no-store, must-revalidate"}
}
}"