When testing with AspDotNet Storefront you may receive the following error:
SGS-020005: Error (Merchant config file is missing, empty or cannot be read)

You can not use the staging server until you setup a separate test account.
You will receive an email that contains a new store number for testing and you will also need to download another PEM file for the test account.
When you are done testing don't forget to change the store number and also replace the PEM file.