For some reason the MarcGermain Show posts are all working. Other podcasts are not currently.
I can observe this too.
I downloaded the latest Film Fustians episode and added it to a post in my local test blog. Afterwards I tried play the episode with the 1PixelOut player in Firefox and the HTML5 audio player of the IE 9. The result is that both player played the episode -> it seems that the files are not the problem.
I have also added the file with the URL of the original location (an URL of the file at your blog) to my local post. The problem occurs in this case. The player has problems playing this remote file.
Since it is not a problem with the file itself, I guess that the problem is connected with the location of the files (the server and its configuration maybe).
But I discovered a confusing thing. I switched off the HTML5 support in my blog so that the blog posts show always (in every browser) the flash player. I could observe that the flash player in IE8, IE9 and Chrome (22.x) did play the remote file. But Safari and Opera had a problem playing this file.
I have no idea why this happens. I can only say that when I place one of your files on my server it plays in all browsers and players.
That is why I still think that it has probably something to with the server configuration.
Maybe you need to add mime-types of the mp3 files to the configuration file of the server (e.g. see http://search.cpan.org/~lds/Apache-MP3-4.00/MP3.pm#DESCRIPTION). But no expert for server configuration.