I have a MSI which is being pushed out through a GPO. It should install as soon as the user logs in. All other MSI's will behave in this way. This one will not install until a reboot.
You may be attempting to overwrite a file already present, but which is locked by another process. In that situation, the MSI Service notes that and triggers the appropriate actions. Refer to the "System Reboots" section of the Windows Installer help to get more detailed info on the actions and properties involved.
