A reboot from a previous installation is pending

When update server or cumulative update in case of exchange updates you can get this error :

A reboot from a previous installation is pending. Please restart the system and then rerun Setup

The Server is reading the following registry keys to determine whether a system restart is required after installation or removal of a software update such as a security update, critical update, or hotfix.

HKLM\SOFTWARE\Microsoft\Updates\UpdateExeVolatile

HKLM\SYSTEM\CurrentControlSet\Control\SessionManager\PendingFileRenameOperations

The Solution is :

To remove an orphaned UpdateExeVolatile registry key value

1. Open a registry editor, such as Regedit.exe or Regedt32.exe.
2. Navigate to HKLM\SOFTWARE\Microsoft\Updates\
3. In the right navigation pane, double-click the UpdateExeVolatile key.
4. Configure the key with a value of 0
5. Close Registry Editor.

To delete the orphaned PendingFileRenameOperations registry key

1. Open a registry editor, such as Regedit.exe or Regedt32.exe.

2. Navigate to HKLM\SYSTEM\CurrentControlSet\Control\Session Manager\
3. In the right navigation pane, right-click the PendingFileRenameOperations key and select Delete.
4. Close Registry Editor.

Now try again !

Good Luck