Some SOE-related sites for games such as Everquest, Everquest 2, Landmark and H1Z1 were also apparently affected.
SOE President John Smedley tweeted that the company had failed to pay its website bills.
"The payment notifications went to a junk email box," Smedley tweeted, adding, "Someone left and it got caught in the replacements junk filter. Simple as that. Embarrassing as that. No point dodging."
"DNS problems could take up to 48 hours to resolve," he wrote, adding, "We are really really sorry on this one folks. Embarrassing and preventable. We screwed up."
"The login issues reported this morning have begun to be resolved," an SOE community relations staffer wrote in a forum post on Tuesday.
"However, some players may be unable to connect to SOE services intermittently for up to 48 hours, including websites, forums and games. We apologize for the inconvenience."