Usually this is the result of an install or upgrade of security software.
You may want to consider what has been installed or upgraded or otherwise reconfigured on the 64 bit machine since the beginning of April.
It's often and most likely third party security suites but may even be a result of tweaks that you, someone or something has made to the native windows firewall.
My general suggestion would be to uninstall any third party security suite software first by using the programs and features applet in the control panel, followed by the vendor specific proprietary removal tool.
You can Google for that or check here Link Removed although I'm not sure that, that list is current and up to date. Your best bet to get current vendor...