It works fine for me when I put the various parameters in the following order...
Code:
rtmpdump -r -a -f -W -p -y -o -C S:username -C S: broadcaster_name -C S:2.607 -C S:password -v -T
And secondly, I would create a %filename% variable outside the rtmpdump command with the date and time formatted and then pass that in as a single variable. It's just less crap to go wrong inside the command and you can echo the filename before you start the rtmpdump command to make sure it's all working (especially if you are having problems with the -o parameter).