asp.net cant login or signup

whenever i try to login or signup on my page i get this error:

Cannot open user default database. Login failed.
Login failed for user 'sa'.

here is my connection string:

   <remove name="loginserver"/>
    <add name="loginserver" connectionString="Data Source=AHMED-PC\SQLEXPRESS;AttachDBFilename=|DataDirectory|asp开发者_高级运维netdb.mdf;Persist Security Info=false;User ID=sa;Password=123456" providerName="System.Data.SqlClient"/>

            <providers>
            <remove name="AspNetSqlMembershipProvider"/>
            <add name="AspNetSqlMembershipProvider"
                 type="System.Web.Security.SqlMembershipProvider, System.Web, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a"
                 connectionStringName="loginserver"
                 enablePasswordRetrieval="true"
                 enablePasswordReset="true"
                 requiresQuestionAndAnswer="false"
                 applicationName="/"
                 requiresUniqueEmail="true"
                 minRequiredPasswordLength="6"
                 minRequiredNonalphanumericCharacters="0"
                 passwordFormat="Encrypted"
                 maxInvalidPasswordAttempts="5"
                 passwordAttemptWindow="10"
                 passwordStrengthRegularExpression=""/>
        </providers>    

i am usually able to login or signup normally but suddenly i started getting this error.

so what is the problem , thanks

just deleted the aspnet.mdf from sql express and now it works