OK, I looked into this issue on his server and what happened is that he placed an IP in the Protector's whitelist for Webmasters:
By doing it, he basically blocked all Webmasters who tried to login from other IP than the one he entered, incl. himself, if he tried to login from a different PC, or if his IP was dynamic and has changed.
To solve the issue, you have to go to the Protector's /configs directory:
and look for a file starting with "group1ips":
In case, there are more of them, look for the one with the latest date, as it is the current one.
Normally, as a default, there should be only this entry inside:
but in his case we had this IP that he entered before:
After replacing it to the default, every Webmaster was able to log in normally.
So if you would like to add IP of Webmasters to the white list, make sure that you enter the info of ALL Webmasters, and that these IPs won't change.
From Ohio, USA