"Connection was reset" when trying to login to CP with EE3

Hi

We have been running EE2 fine for the past 4-5 years on our local Windows / Apache platform. However since trying to install EE3.4.1, when we try to login to the admin control panel we are getting:

"The connection was reset"

The Server Wizard shows everything as fine and it works on our remote development platform no problem. But we are just unable to pinpoint the cause of this problem.

If anyone is able to share any knowledge on what be the problem, it would be so appreciated.

Thanks, Jonathan