Before you say "there are 100 other threads about this", I have looked around and not found a fix that works for me.
I don't know exactly what info I need to tell you in here, other than messages worked fine for me on 10.8.5, then upgraded to mavericks when it released and I cannot log in. Originally I was getting a "An error occurred during activation. Try again." None of the solutions I attempted caused a changed in this error, except when I changed my appleID password. Now I am just getting a hang when I try to log into iMessage, but still no successful login.
I am using Chimera 2.2.1 (which i think bundles the most recent chameleon). Everything I read says that this boot loader is supposed to fix the iMessage issue but it seems not to in my case. I have gone through the replacing the FileNVRam and having the nvram.plist regenerated. I don't know exactly what is supposed to be in this plist (forums I have read seem to give sporadic advice about this). I realize that to receive help, I probably need to post more information for you, but I don't know what that is at this point.
Thanks in advance for any help you can offer, as I am out of ideas on how to proceed. Will update this thread if I find a solution.
UPDATE: Fixed using the official chameleon from the downloads section on this site, instead of chimera. This did not work for me the first few times I had tried, so YMMV on this? Not exactly sure why it fixed it on the 3rd of 4th try.