Billing Address was not provided error

Hi,

We are on Nop 1.6 and are getting a SPORADIC error during checkout.  

When you go thru the one-page checkout and get to the final step and then press "Confirm", the error "Billing Address was not provided" occurs and the checkout does not complete.

This only happens about 1 time in 10 or so but we can't figure out why, after you enter your billing info and go to the next screen and then the final screen you might lose that info.

We could upgrade to 1.9 if needed but not 2.x because we can't run MVC in our CMS.  We didn't find any other people with this problem in the forums so we are not sure if an upgrade would help.

Let us know if you have any suggestions or have seen this before

Thanks

Ben

I`ve just got this error on onepagecheckout in V2.2

The problem is in the commented line

  public virtual void SetBillingAddress(Address address)
        {
            if (address != null)
            {
               // if (this.Addresses.Contains(address))
                    this.BillingAddress = address;
            }
            else
            {
                this.BillingAddress = address;
            }

        }