PTR Character Copy issues have halted players from testing patch 2.3—for this matter Hortus has posted an acknowledgement. The team knows about the issue and are working to resolve the issues. I just tried right now copying my character at 2:30pm EST. No luck yet. Keep trying or check back for an update. Since I am trying, I wll let you know when it works. Make sure to check out WorldofRaids for screenshots of new mounts and loot.
Hortus: We are aware that players are having problems with the character copies this is being investigated
Source: Wow PTR Forums