xmlrpc.php errors (pingback, wbloggar and so on)

I use WordPress 1.0.2. If I try tools like blogjet or wbloggar oder moblog/vagablog (for palm) I get error messages which have to do with “xmlrpc.php”. This messages say something about “invalid payload”. So for example here is the message from a b2evolution-blog which tried to pingback an entry of my WordPress blog:
Processing: https://medienfakten.de/content101/
Connect to server at: medienfakten.de
Pingback server found from X-Pingback header: https://medienfakten.de/content101/xmlrpc.php
Page Linked To: https://medienfakten.de/content101/
Page Linked From: https://b2evolution.net/demo/blogs/blog_a.php/2004/04/11/p37-Weblogs_f_r_Anf_nger2
Pinging medienfakten.de…
Remote error: Invalid return payload: enabling debugging to examine incoming payload (2)
What das “payload” mean?