Check the following:
- Provider(s) listed in EnabledProviders of the Service
web.appSettings.config? (Check your spelling too)
- The settings for each enabled shipping provider are present and set
with valid account/key data?
- The Provider(s)' DLLs, XMLs and PDBs are present in the plugins
folder?
- The plugins folder is at the correct path?
- The Dimensional vs Non-Dimensional Weight settings match the data
for the product packages?
- The products actually have packages with data on them?