Configuration problems

Hello,

We're trying to create our nop store but we're having serious problems. Everyone is getting crazy around here.
Never though this could be so difficult...
First we had a "tax provider" error, now this:


Server Error in '/' Application.

Value cannot be null.
Parameter name: type

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.ArgumentNullException: Value cannot be null.
Parameter name: type

Source Error:

An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below.

Stack Trace:


[ArgumentNullException: Value cannot be null.
Parameter name: type]
   System.Activator.CreateInstance(Type type, Boolean nonPublic) +7469174
   System.Activator.CreateInstance(Type type) +6
   NopSolutions.NopCommerce.BusinessLogic.Tax.TaxManager.GetTaxRate(ProductVariant productVariant, Int32 taxClassId, Customer customer, String& error) in F:\Temp\Test\nopCommerce 1.60\Libraries\Nop.BusinessLogic\Tax\TaxManager.cs:326
   NopSolutions.NopCommerce.BusinessLogic.Tax.TaxManager.GetPrice(ProductVariant productVariant, Int32 taxClassId, Decimal price, Boolean includingTax, Customer customer, Boolean priceIncludesTax, String& error) in F:\Temp\Test\nopCommerce 1.60\Libraries\Nop.BusinessLogic\Tax\TaxManager.cs:464
   NopSolutions.NopCommerce.BusinessLogic.Tax.TaxManager.GetPrice(ProductVariant productVariant, Decimal price, Boolean includingTax, Customer customer, String& error) in F:\Temp\Test\nopCommerce 1.60\Libraries\Nop.BusinessLogic\Tax\TaxManager.cs:425
   NopSolutions.NopCommerce.BusinessLogic.Orders.ShoppingCartManager.GetShoppingCartSubTotal(ShoppingCart cart, Customer customer, Decimal& discountAmount, Discount& appliedDiscount, Boolean includingTax, Decimal& subtotalWithoutPromo, Decimal& subtotalWithPromo) in F:\Temp\Test\nopCommerce 1.60\Libraries\Nop.BusinessLogic\Orders\ShoppingCartManager.cs:496
   NopSolutions.NopCommerce.BusinessLogic.Orders.ShoppingCartManager.GetShoppingCartSubTotal(ShoppingCart cart, Customer customer, Decimal& discountAmount, Discount& appliedDiscount, Decimal& subtotalWithoutPromo, Decimal& subtotalWithPromo) in F:\Temp\Test\nopCommerce 1.60\Libraries\Nop.BusinessLogic\Orders\ShoppingCartManager.cs:467
   NopSolutions.NopCommerce.Web.Modules.MiniShoppingCartBoxControl.GetOrderSubtotal(ShoppingCart shoppingCart) in F:\Temp\Test\nopCommerce 1.60\NopCommerceStore\Modules\MiniShoppingCartBox.ascx.cs:98
   NopSolutions.NopCommerce.Web.Modules.MiniShoppingCartBoxControl.OnPreRender(EventArgs e) in F:\Temp\Test\nopCommerce 1.60\NopCommerceStore\Modules\MiniShoppingCartBox.ascx.cs:70
   System.Web.UI.Control.PreRenderRecursiveInternal() +80
   System.Web.UI.Control.PreRenderRecursiveInternal() +171
   System.Web.UI.Control.PreRenderRecursiveInternal() +171
   System.Web.UI.Control.PreRenderRecursiveInternal() +171
   System.Web.UI.Control.PreRenderRecursiveInternal() +171
   System.Web.UI.Control.PreRenderRecursiveInternal() +171
   System.Web.UI.Control.PreRenderRecursiveInternal() +171
   System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +842

Version Information: Microsoft .NET Framework Version:2.0.50727.4214; ASP.NET Version:2.0.50727.4209





What should we do?