While we were upgrading one of our VCSA 6.5 vCenter appliances to 6.5 Update 1, I ran into an error Stage failed when trying to check for updates within the port 5480 admin interface.
Since we’ve had an ongoing issue of java crash dumps filling up the disk space I checked the /storage/core/ partition with df and found it was 100% used. I erased the java .jsvc coredumps to free up space and reran the Check for Updates option.
This seemed to have been the issue. Hopefully future error statements will be a bit more verbose.