How to get e-mail address with yahoo?

How do I get a valid format email address. I have Yahoo but when I use it for other things it says not valid.

• When I use my yahoo email address it says not a valid email format address. How can I get a valid format email address to other things other than the usual mail

• Answer:

  Yahoo is still having some problems at the moment. Suggested cures range from Update Adobe Flash Player and Javascript to clear IE7 cache, cookies, and browsing history. Different things seem to work for different people. It's causing attachments to not show, 999 errors where it won't let you do a particular action and some people cannot send recieve delete or move mail. It's not just Vista either it's happening to some of us on XP. I have been advised to use this site to view my mail, www.mail2web.com if all else fails go back to classic mail via this link. http://us.mg1.mail.yahoo.com/dc/optout?script=no click yes when asked do you want to opt out. Hope this helps.