I just recorded a 147 Mb .flv video from Google with WM Recorder 12.0 in the ADA mode. I had no any problem. I just did the following:

1. Started WM Recorder. Switched to the ADA Auto recording mode .
2. Opened my Firefox and navigated to the google video.
3. Played the video in the embedded flash player.
4. As soon as WM Recorder started recording the video, I stopped playing it in the embedded player.

What version of WM Recorder do you have?

Do you know that there are lots of other ways to record HTTP flash .FLV videos? One of them is by using freeware Miro.