Hmmm - pretty much everything looks good but the playback of the buffer file.
The way the plugin works is that it starts writing the audio to an mp3 buffer file then tells pvrx2 to start playing back the file. The following from your DvbtrClient.log shows it's trying to play gbnetradio-0.mp3 but something is going horribly wrong.
Can you confirm that you have an I:\Videos\Recordings\gbnetradio-0.mp3 file? If so can you play it with Windows Media Player or anything else you use for mp3 files?
06/10/2008 23:32:09.050 Invoking PlayAudioFile() for I:\Videos\Recordings\gbnetradio-0.mp3
06/10/2008 23:32:09.191 Play2() threw exception: [cut]
Is I: a network or local drive? Is it NTFS - if so does the Local System account have full read/write access to it?
Looking at other bits in the logs, it looks like something has possibly gone screwy with the DvbtrService so you may want to restart that before trying anything else.