IT means that the information for connecting to the Fed Ex server that you entered is not correct and the fed ex server is not allowing you access.
NOTE: FEd Ex made some updates to their API Recently, We Have just released eCart 5.0.7 to address these changes.
you should uninstall eCart from the extension manager, then install the new update. in the WA_eCart folder delete the fed ex helper file, then edit the fed ex shipping server behavior on the confirm page to correct the settings and have the new fed ex file generated.