I'm just adding my name to the list of people who are having the following error:
"Login error: Cannot reach the Nexus login server. Either your firewall is blocking NMM or the login server is down."
I've tried reinstalling NMM, updating it (already up-to-date), and adding exceptions to my firewalls (Windows and Bitdefender). The problem is still happening, and judging by the numerous other posts yesterday and today of this issue, I guess it must be a server-side issue.
Please fix this! Thanks!