xml-rpc fails with cryptic error message

If someone will help me track the source of this error down, I’ll do the grunt-work.

Trying to upload a .pdf file (and some other file types) from a blog client (so far, they give the same error) the upload fails with the following error message:
XML Parsing Error: Invalid procedure call or argument

This is with a Direct Upload (as the blog clients call it) but with FTP, it works okay.

Looks to me like some more logging needs to be put in xmlrpc.php, but I haven’t figured out where to add logging/debug output… it would be helpful to know what procedure was called, and with what arguments.

Here’s one of the xmlrpc.php log, in case it helps:

2007-07-20 19:31:07  Input: <?xml version="1.0" encoding="UTF-8"?>
<methodCall>
  <methodName>metaWeblog.newMediaObject</methodName>
  <params>
    <param>
      <value>
        <string>1</string>
      </value>
    </param>
    <param>
      <value>
        <string>nimda</string>
      </value>
    </param>
    <param>
      <value>
        <string>******</string>
      </value>
    </param>
    <param>
      <value>
        <struct>
          <member>
            <name>name</name>
            <value>
              <string>/wp-content/uploadstestpdf.pdf</string>
            </value>
          </member>
          <member>
            <name>type</name>
            <value>
              <string>application/pdf</string>
            </value>
          </member>
          <member>
            <name>bits</name>
            <value>
              <base64>JVBERi0xLjQKJcOkw7zDtsOfCjIgMCBvYmoKPDwvTGVuZ3RoIDMgMCBSL0ZpbHRlci9GbGF0
ZURlY29kZT4+CnN0cmVhbQp4nLWUTWvDMAyG7/kVOheWSfI3lEHTj3shsD+wdbDDYL3s7++1
snipped for at least SOME brevity...
IFIKL0lEIFsgPEZGNTY4RkYzNTE0RUE4QzhFNjUzM0VGRDVBNUJDMzU1Pgo8RkY1NjhGRjM1
MTRFQThDOEU2NTMzRUZENUE1QkMzNTU+IF0KPj4Kc3RhcnR4cmVmCjMyMzAxCiUlRU9GCg==
</base64>
            </value>
          </member>
        </struct>
      </value>
    </param>
  </params>
</methodCall>