I'm having the exact same problem. Hosted on Wordpress.com. Have put in all the info according to the various workarounds on the Diigo site and still can't stop getting 1503 errors.
Is there no way to set up the blog for autoposting without having to give Diigo access to my wordpress.com account?
Is there no way to set up the blog for autoposting without having to give Diigo access to my wordpress.com account?