Getting a System.NullReferenceException error after updating to v 1.7

Thanks. The link helped to fix it. Now I get this error:

Error  55  Could not load file or assembly 'Nop.BusinessLogic' or one of its dependencies. The system cannot find the file specified. (C:\inetpub\wwwroot\nopCommerce_1.70_Source\web.config line 25)  C:\inetpub\wwwroot\nopCommerce_1.70_Source\NopCommerceStore\Administration\Modules\SpecificationAttributes.ascx  16  


Error  59  Could not load file or assembly 'Nop.BusinessLogic' or one of its dependencies. The system cannot find the file specified. (C:\inetpub\wwwroot\nopCommerce_1.70_Source\web.config line 25)  C:\inetpub\wwwroot\nopCommerce_1.70_Source\NopCommerceStore\Administration\Modules\AffiliateOrders.ascx  5  

Error  60  Could not load file or assembly 'Nop.BusinessLogic' or one of its dependencies. The system cannot find the file specified. (C:\inetpub\wwwroot\nopCommerce_1.70_Source\web.config line 25)  C:\inetpub\wwwroot\nopCommerce_1.70_Source\NopCommerceStore\Administration\Modules\AffiliateOrders.ascx  6  


Where is the web.config file should be located?

My web.config file is located in C:\inetpub\wwwroot\nopCommerce_1.70_Source

I found that when I add a picture in Product Variant the System.NullReferenceException error disappears.

Now how do I fix this ?