I've managed to track down the root of the problem that I was experiencing using the Newzcrawler 1.5.2 beta and posting to Blogware.

Complete details of the fix can be found here: http://www.newzcrawler.com/forum/viewtopic.php?t=57&highlight=error

The essence is that this new build was passing the wrong encoding to the server which was rejecting it. Changing this to UTF-8 fixes the problem. There are some new Moveabletype API errors that are being generated - I will document these later and submit as bug reports.

Glad to see that the problem was with someone else's software.