Board Thread:Technical Support/@comment-97.93.5.102-20160115060425/@comment-27413644-20160115064001

"October 10, 2015: 2.0 users cannot browse online levels. This feature was added to force users to update to the latest version, in this case, 2.01. If a user is not playing in the most current version, they cannot browse online levels."

(from: http://geometry-dash.wikia.com/wiki/Update_2.0)

You are most likely still on 2.0. The latest version is 2.01, and I can browse GD levels and map packs without any problem. From October 10, 2015 onwards, loading user levels for 2.0 users will be terminated, while 2.01 users remain fine.

If you are on 2.01, I'm not sure. And GD 2.1 is not out yet - RobTop is still working on it and 2.1 is set to be released in February 2016.