I got a null reference exception on a Linq To SQL data context and I don't even really know where to start

I just deployed a users and roles asp database to a website and I'm getting this exception

Object reference not set to an instance of an object. Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: System.NullReferenceException: Object reference not set to an instance of an object.

Source Error:

Line 41:   #endregion
Line 42:    
Line 43:    public UsersAndRolesDataContext() : 
Line 44:                base(global::System.Configuration.ConfigurationManager.ConnectionStrings["ConnectionString"    ].ConnectionString, mappingSource)
Line 45:    {


Source File: d:\hosting\7122544\html\SSM\App_Code\UsersAndRoles.designer.cs    Line: 43

Stack Trace:

[NullReferenceException: Object reference not set to an instance of an object.]
   UsersAndRolesDataContext..ctor() in d:\hosting\7122544\html\SSM\App_Code    \UsersAndRoles.designer.cs:43
   admin_ManageUsers..ctor() in d:\hosting\7122544\html\SSM\admin\ManageUsers.aspx.cs:11
   ASP.admin_manageusers_aspx..ctor() in c:\windows\Microsoft.NET\Framework\v4.0.30319\Temporary ASP.NET Files\ssm\5b123e8f\6bb9cf4c\App_Web_tz5adhff.10.cs:0
   __ASP.FastObjectFactory_app_web_tz5adhff.Create_ASP_admin_manageusers_aspx() in     c:\windows\Microsoft.NET\Framework\v4.0.30319\Temporary ASP.NET Files\ssm\5b123e8f\6bb9cf4c\App_Web_tz5adhff.12.cs:0
   System.Web.Compilation.BuildResultCompiledType.CreateInstance() +32
   System.Web.Compilation.BuildManager.CreateInstanceFromVirtualPath(VirtualPath开发者_如何学Python virtualPath, Type requiredBaseType, HttpContext context, Boolean allowCrossApp) +109
   System.Web.UI.PageHandlerFactory.GetHandlerHelper(HttpContext context, String requestType, VirtualPath virtualPath, String physicalPath) +31
   System.Web.UI.PageHandlerFactory.GetHandler(HttpContext context, String requestType, String virtualPath, String path) +37
   System.Web.MaterializeHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +334
   System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +184

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You are likely missing connection string, named ConnectionString in the config file, so System.Configuration.ConfigurationManager.ConnectionStrings["ConnectionString" ] returns null.

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You may be missing a connection string in your Web.config or App.config. Make sure that you have something similar to the following in your file.

<connectionStrings>
    <add name="AdventureWorksEntities" 
         connectionString="metadata=.\AdventureWorks.csdl|.\AdventureWorks.ssdl|.\AdventureWorks.msl;
         provider=System.Data.SqlClient;provider connection string='Data Source=localhost;
         Initial Catalog=AdventureWorks;Integrated Security=True;Connection Timeout=60;
         multipleactiveresultsets=true'" providerName="System.Data.EntityClient" />
</connectionStrings>