I have the same problem with WM Recorder. I don't really know how to solve it. May be I just need to reboot my computer. I have contacted the developer already.

However I had no any problem with two other stream recorders I have tried:
Replay AV captured rtsp:// .ra link without any problem and I was able to save the stream to hd successfully.

NetTransport works differently: it can process .ram metafile and start downloading from the URL immediately. The stream was also saved to hd successfully.