Windows 8.1 is not yet final so is not officially supported by any McAfee software. However I think I need to move this thread to Enterprise.
What McAfee product is this and is it in ePO?
Product is: SaaS Endpoint & Email Protection
I have a Grant number but am not sure what you mean by EPO
That's OK. I've moved this provisionally to Business > SaaS for better support.
Windows 8.1 is not compatible with SaaS Endpoint Protection.
For more details, please view the below mentioned KB Article.