The computer couldn't connect to the login server because a security program was blocking the connection, or because the connection was unstable.
Try closing background applications to resolve any software conflicts.
Configure your security software's exception list to allow Blizzard applications to run.
Reset your network devices to make sure your router hasn't become flooded with data.
Release and renew your IP and flush your DNS to resolve any network conflicts.
Run a security scan to remove any viruses or malware infections.
Note: A malware program called Scorpion Saver may cause this error. It's difficult to remove and may not be caught by normal antivirus scans. To identify an infection, gather your MSInfo and check Software Environment -> Loaded Modules for "Adpeak." If it appears on the list, contact a certified computer technician in your area for assistance removing the program.