I had this error as well and employed the re-registration solution, but without success.
However, when I had the firewall team open up the rule for allowing ICMP to 72.163.7.113/443 for a one-time validation for Cisco portal connectivity, the upload worked.
Originally, this is a one-time need for when CSPC appliances are initially spun up. It would seem that this is built into the code for CSPC to use ICMP as a means for validating connectivity to the Cisco portal before proceeding further with any upload procedures. Once it's done, connectivity is validated for the life of the appliance.
However, following this event, it would seem that this is not a lifetime validation. As a result, it may run on a fixed timeline of validation running into years with the occasional need to "re-up" this validation of connectivity.
Either way, our system is now functional as needed again thanks to this process. Hopefully, this will help someone else with the same issue in the future.
