Getting Page Not Found re-direct on subsite login

Hi guys

After I upgraded to 4.0 everything appeared to go smoothly, however I’ve just received an email from one of the sub site users saying they keep being re-directed to a Page Not Found URL when they try to login to the sub site dashboard.

So, I tried & am geting the same thing on all sub sites (using folders not sub domains), but, if I login to the main site I can access the sub sites via the My Sites dashboard.

Any suggestions?

Oh, this is the URL that was 1st pointed out to me as re-directing
https://www.menvcity.org.uk/gm/wp-admin