Hi all, I have an early-2011 MBP, running 10.8.4 and Snow Leopard 10.6.8 (dual boot). On Snow Leopard, I use iChat with an AIM account. This allows me to use text chat, audio and video chat, and screen sharing as well. On Mountain Lion, I use Messages with the same AIM account. Text chat works, but I can't use audio nor video : when I try to call a contact, or when a contact tries to call me, it displays "connecting..." but never manages to connect. I have tried many, many things (can't list them all) as deleting .plist files, account, caches, repairing permissions, using Onyx, and even.... re-installing 10.8.4 (!!)... unsuccessfully. Then, I tried this : On an external hard drive, I installed a fresh 10.8.4 from my USB stick, launched Messages, added my AIM account and tried audio and video calls with a relative... it worked ! The day after, I booted again from the external hard drive and tested again : audio and video no longer worked, text was ok. Strange indeed.... Booted from Snow Leopard : all worked. Booted again from the external hard drive : text only. It sounded so strange that I decided to erase the "fresh" 10.8.4 on the external hard drive, and installed it again. Tested Messages : audio and video worked.... Rebooted the computer and tested again : audio and video no longer worked, text only. So, here is my conclusion : audio and video in Messages work only the FIRST time I use it. Then, it no longer works, it is text only. Sorry for the long post and my terrible English, and thank you in advance for your help.