Just verify your E-mail address. According to yahoo's new e-mail policies All users should reverify their e-mail addresses. I also happened that last week and after verifying it resolved.
Seen those internet marketers found out that Yahoo Answer is their gold mind for traffic, they do whatever they do for getting search engine notice, create multi-account, answer them-self, vote, cheat... soon the Yahoo Answer tool was frustrated and they have to do something to solve the problem.
Many people use Yahoo answers to help promote their own or their friends' businesses and websites. However, if you promote too heavily, or in a way that seems like spam, your Yahoo Answers account can be suspended or permanently closed without warning.