In some environments, the Symantec Installation Manager (SIM) upgrade is taking a very long time.
ITMS 8.x
While this can be valid for a slow machine, it has been found that pending reboot requirement causes Windows MSInstaller to work very slowly.
Try rebooting the machine prior to the upgrade. This should resolve this issue in most cases.
When SIM is launched it may show up a message that a reboot is required.