If you get caught out by the (vague) error of "Windows Updates fail to install - Error code: 1625", after much searching I found this solution worked in most scenarios:

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start > run regedit

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Browse the registry to HKLM\Software\Policies\Microsoft\Windows\Installer

Create: DisableMSI

Type: REG_DWORD 　value = 0 　 (0 should allow you to install it was originally 1)

(In my case the value had been set to 2 so I changed it to 0)