Question: I am using Spree version 2.4.2. I want the Indian Rupee currency instead of US Dollars. In the admin panel, I changed the US Dollars setting to Indian Rupee and it is throwing the error "We are unable to calculate shipping rates for the selected items.".

Answer: 
You need to ensure that your shipping method is configured correctly. If you have an order that costs ₹500 and the shipping methods are all configured in USD, it won't be able to find an appropriate shipping method. Your shipping method calculator must also store its cost in rupees.
To change currency in **spree**

In `config/initializers/spree.rb`

change `config.currency = "USD"` to `"INR"`

And in `spree` admin change you shipping method currency.

It will work for me, I think It also work for you.