Hi,

Not sure if this has been reported yet (looked but didnt see).  All I did was as follows:
o downloaded and extracted nopCommerce2.40 onto a new folder
o copied Settings.txt file from nopCommerce2.30 App_Data folder onto nopCommerce2.40 corresponding folder
o created backup of nopCommerce23 database
o restored backup of nopCommerce23 database onto nopCommerce24
o ran the upgrade.sql script
o started VS and ran it
o The default store is displayed without issues
o Click on New Products and get the following:

Object reference not set to an instance of an object.

on line 239 of the TaxService.cs file

            //get tax rate
239      var calculateTaxResult = activeTaxProvider.GetTaxRate(calculateTaxRequest);
            if (calculateTaxResult.Success)
            {
                //ensure that tax is equal or greater than zero
                if (calculateTaxResult.TaxRate < decimal.Zero)
                    calculateTaxResult.TaxRate = decimal.Zero;
                return calculateTaxResult.TaxRate;
            }

You apparently wont get this error if you have one or more tax providers installed.  I installed the StrikeIron provider and reran the code and it ran fine this time.  I would imagine that most folks wont be running into this since they'll have at least one tax provider.