Hello,

well this problem seems to be pretty common, especially with downloaded files from the internet, so here is how you can fix it:

• browse to http://www.mplayer.at ( download mplayer + mencoder for your OS, its available for Windows too )
  (there is no installer, you just need to extract the files from the archive to c:/program files/mplayer or similar)
• put the broken movie into the same directory ( makes things easier for you )
• now open a command shell ( for our Windows Users: Start -> run -> cmd )
• change into the directory where you put mplayer and the movie
• now run one of the following commands (replace the file names accordingly)
  
  mencoder file.avi -forceidx -oac copy -ovc copy -o fixedfile.avi
  
  mencoder file.avi -noidx -oac copy -ovc copy -o fixedfile.avi
  ( in some cases the upper one works best, in some the lower one, try both before you give up! )
• mencoder will now work for a while, after its done the movie should be properly working