there is nothing wrong with your command line. i am able to download successfully with your posted command line. rtmpdump tries to save Player Hash in .swfinfo file. on your system something is blocking it to doing so. try running with admin privileges or turning your antivirus off.
Code:
RTMPDump v2.4 GIT-2012-03-08 (Compiled by KSV)
(c) 2010 Andrej Stepanchuk, Howard Chu, The Flvstreamer Team; license: GPL
Connecting ...
INFO: Connected...
Starting download at: 0.000 kB
INFO: Metadata:
INFO: duration 3906.54
INFO: moovposition 28.00
INFO: width 640.00
INFO: height 360.00
INFO: videocodecid avc1
INFO: audiocodecid mp4a
INFO: avcprofile 77.00
INFO: avclevel 31.00
INFO: aacaot 2.00
INFO: videoframerate 0.00
INFO: audiosamplerate 22050.00
INFO: audiochannels 2.00
INFO: trackinfo:
INFO: length 351586980.00
INFO: timescale 90000.00
INFO: language eng
INFO: sampledescription:
INFO: sampletype avc1
INFO: length 351588510.00
INFO: timescale 90000.00
INFO: language eng
INFO: sampledescription:
INFO: sampletype mp4a
1059.772 kB / 4.44 sec (0.1%)