I just saw that the experiments on the previous post's title seem to have caused many superfluous trackback pings to be sent. My apologies for that.
I'll try to shift part of the blame to MovableType and Safari. I frequently have the problem that Safari times out on MT as our servers seems to run the scripts rather slowly at times. Also, Safari sometimes doesn't seem to be too keen on updating pages that it already cached earlier. Together these lead me to think there actually was an error and hit 'post' again... generating two posts.
The same this time. Due to the error messages I thought the posts weren't generated at all, but it turned out that MT apparently did everything – update its database, update the index pages and ping people – before running into the filename error.
Received data seems to be invalid. The wanted file does probably not exist or the guys at last.fm changed something.