DV Info Net - MPEG Streamclip

I recently downloaded this software and installed QT 1.81. I have some video files that I needed to encode at a smaller file size. My method of working with my video files was 1. Use Pavtube software to merge my JVC HD video files into 1 file, then 2. Use MPEG Streamclip to re-encode these files down to a smaller size while keeping the same video quality, then 3. Use Wondershare Video Editor to load up the video file and detach the audio part of it and delete, then add my MP3 audio of the same recording and add it to the video, thus have a good quality sound file instead all of the surrounding sound the video cam mic picked up, then 4. Use MPEG Streamclip to re-encode this new file to a smaller file size. This procedure worked great for the first 4 video files that I had. Then I started working with video file # 5 and then I started getting the following error message in MPEG Streamclip: "Error: cannot write the movie file" at the end of the conversion process. Any ideas why this error would show up later on? I have uninstalled QT 1.81 and reinstalled it. I have installed QT 1.76 and I still get the same error message. Oh and I am using Windows 7 64-bit, on a Toshiba laptop with AMD A6 chip. And I have plenty of hard drive space and I have also an external 2 GB hard drive as well...