On my blog, I’ve recently posted the first part of an article on how to solve many of these problems by first identifying them precisely using the log file of WLW and/or an HTML traffic capturing tool such as Fiddler:

http://coding-paparazzi.sylvainlafontaine.com/2010/02/solving-connection-problems-wlw.html

Beside the log file and Fiddler, this part one covers the specific problems of the presence of a an UTF-8 BOM at the beginning of one of the PHP script files (often, this will be the wp-config.php file in the case of WordPress) and of the presence of extraneous characters at either the beginning (before the opening tag ) of one of the PHP script files.

In the second part (soon to be published), I will cover the problem of the presence of Warning and of Fatal PHP error messages in the XML-RPC response file. Fatal errors are usually the result of some kind of error in the PHP code but you can get a Warning error message simply by having a badly set php.ini file; so it’s often simply a local configuration problem of PHP.

I just replaced xmlrpc.php file with the same file, but from version 2.6.3 and it works!