We recently ran into in issue with Fax Services installed on a Windows 2003 server. Everything was working fine up until the beginning of the month 03/01/15 and then from any Windows 7 computer using Fax and Scan it is unable to contact the fax server that is installed as a fax services on the Windows 2003 Server. When you go into Fax Accounts it says disconnected.
So in troubleshooting I tried to remove the Fax Server on the Windows 7 pc under Fax and Scan > Fax Accounts then go back and re-add. When I went back to re-add I get the message "You do not have security permissions to complete this operation. Contact your fax administrator for more information."
Now I checked all permissions, that worked for awhile before they stopped working and made sure the users were added that were needed for permissions to this fax server. I even added everyone, anonymouse logon, network service just to be sure and still nothing.
It is like a policy got turned on or extra security layer in a windows update or something.
Now I can login as the Administrator on the network and am able to add this Fax Server without issue.