Edouard,
Many thanks for your reply. I checked the keychain value (it appears to only store the password) and it appeared to be OK. But that was to be expected since I had already re-wrote the login information and saved those values earlier, so I would assume that if they were corrupted, the re-write would have un-corrupted them. My web host claims there's no block on my IP or any other thing out of the ordinary.
Reading other posts about this issue, it seems there have a been a few times this has occurred. One user simply solved it by going to a different host which would point to the original host as the problem, not WC. I'm thinking of going down that path and see what happens. I'm pretty much out of ideas.