Invalid config field backend model

"Invalid config field backend model: premiumrate_adminhtml/system_config_backend_shipping_premiumrate"

After installing an extension, if an error appears similar to the the one above when trying to save configuration settings, this is usually caused by missing files or a corrupted file.

To resolve this issue, check to make sure that all the extension files have been installed to the right location, ensure you have refreshed caches and also re-compiled if applicable.