Browsers on iMac and Vista give Redirect Loop error on login

This started this morning and I cannot log into my ping account:

"Redirect Loop
Firefox has detected that the server is redirecting the request for this address in a way that will never complete.
The browser has stopped trying to retrieve the requested item. The site is redirecting the request in a way that will never complete.
* Have you disabled or blocked cookies required by this site?
* NOTE: If accepting the site's cookies does not resolve the problem, it is likely a server configuration issue and not you"

I do NOT have cookies blocked or disabled.

Can someone please help? I had to STOP Twitterfeed from updating Ping because of this.

Thanks.