I think ConnectionString Problem you try this code.
Use bellow code in Web.cofig
<connectionStrings>
<add name="OsmEmpConString" connectionString="Data Source=.\sqlexpress;Integrated Security=SSPI;AttachDBFilename=C:\Documents and Settings\Administrator\My Documents\Downloads\Rags_Modified\Rags\Rags\App_Data\Reg.mdf;User Instance=true" providerName="System.Data.SqlClient"/>
<add name="SomeDataBase" connectionString="Data Source=.\SQLEXPRESS; AttachDbFilename=C:\Documents and Settings\Administrator\My Documents\Downloads\Rags_Modified\Rags\Rags\App_Data\Reg.mdf; Integrated Security=True; Connect Timeout=30; User Instance=True" providerName="System.Data.SqlClient"/>
</connectionStrings>
In code behind
string constr = ConfigurationManager.ConnectionStrings["SomeDataBase"].ToString();