If you are having an issue installing a service pack (which actually is a full binary reinstall/upgrade) of exchange 2007 where it prompts you to reboot because another install is in process, it means a registry flag failed to delete previously. To resolve the issue delete the key as follows:
- Open a registry editor, such as Regedit.exe or Regedt32.exe.
- Navigate to HKLMSYSTEMCurrentControlSetControlSession Manager
- In the right navigation pane, right-click the PendingFileRenameOperations key and select Delete.
- Close Registry Editor