Custom Error Message?

I am trying to test the flat rate shipping I have set up in my test environment. Can you please help me understand why I got the message: An error occurred, try again later or contact us. I have the test environment setup for flat rates I have my test environment API Key installed on my site too. The only thing I can think of that is not working is that my cart is not pulling in the weights of the products from my website. I am still using a development environment to build my site and not my actual URL that will house my website.

thank you,

Keith Brenner