All of my users are on 2.6.2. I have uploaded 2.6.3 to the OpenFire server. When some users receive the update notification and hit Yes, it pulls down the installer, prompts to shut down Spark, they hit Yes, Spark shuts down and the installer never runs. I have seen it using both the online and offline installer.
It seems to only be happening on Windows 7 machines. XP machines run it fine.