after successful creation of 3 users on my web site now I can't create users anymore

Happy day to everyone here ! I've got strange situation because after successful creation of 3 users on my web site now I can't create users anymore. I can't do it from CreateAccount.aspx page when it open in Internet, as well I can't do it from asp.netwebadminfiles page on security tab into create user . Error 'Password length minimum: 7. Non-alphanumeric characters required: 1.' But I used password angelikasfriend_35 so it's should be fit to requirements and this password is similar with passwords of previously created 3 others users. Where can be a problem? I would be pleased if someone had same and can tell what to do with it. I am waiting to hear from all of you as soon as possible. Sincerely yours Angelika.
 
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