Hi,
It is not recommended reverting the client back to 7.4 or 7.5 from 7.6.Instead,I suggest you applying KB2720211.
There is a thread talking about the "downgrade" for your reference:http://social.technet.microsoft.com/Forums/en-US/winserverwsus/thread/f3b26ede-7ec8-4ebc-8819-7e1ab389dca4/
Regards,
Clarence
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