I've tried googling and searching everywhere for a solution to my particular problem, but with no luck.
Basically, having upgraded to WordPress 2 from WP1.5 I now find that my site is unable to send trackbacks to other sites (with the url to trackback to simply sitting in the "to_ping" column in the wp_posts table in my database).
Furthermore, incoming/inbound trackbacks do not work correctly. The trackback is 'recorded' in as much as the "comment count" in the wp_posts table is added to, but the actual trackback is not recorded in the wp_comments table.
The result is that some of my posts will say "There have been 4 responses", but because two were trackbacks, only 2 comments actually appear.
I've tried a number of things (including the 'patch' available here: http://blog.serv.idv.tw/2005/12/29/380/
I've also gone through some of the code myself but not seen anything obviously wrong.
If anyone has any ideas on why this might be going wrong and/or what to do to fix it then I'd be most grateful - as it is annoying not being able to trackback to other articles, and doubly-annoying to have to continually check that the "comment count" in the posts table is actually accurate!
Also, if anyone has the same problem then please post and let me know - so that we might learn whether this is an isolated problem, or, as i suspect, a more widespread problem.