error Provider: SQL Network Interfaces, error: 26 - Error Locating Server/Instance Specified??

Using VWD 2005 Express. Built ASP.Net membership site using the ASP.NET Configuration site. Site works on my build pc but I have published it to my hosting provider i get the error  Provider: SQL Network Interfaces, error: 26 - Error Locating Server/Instance Specified. The databse is n the App_data folder. The root directory has write permission.My web.config is (written by the ASP.NET Cnfiguration site). I was told by hosting provider that they do support SQL Express.

 <configuration>
    <appSettings/>
    <connectionStrings>
        <add name="ContactConnectionString" connectionString="Data Source=.\SQLEXPRESS;AttachDbFilename=|DataDirectory|\ASPNETDB.MDF;Integrated Security=True;User Instance=True"
            providerName="System.Data.SqlClient" />
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