Cannot post reliably - keep getting errorsCannot post reliably –keep getting errors

I am having great difficulty in posting anything that is not straight text –I suspect a WordPress bug (recently upgraded to 2.9) but I cannot narrow it down. It appears to be when I have links to external sites. Wonder if WordPress introduced a new security feature?
Got it –any post created with the twitter upload plugin active and WP 2.9 or greater gets garbled. Disable and delete the plugin,then create new posts –all is good.
Set up with different plugins and theme.