AVI files conversion : audio only

[stanzanim]

Using convert / save with some avi files generate a audio only output. For most of them it works i.e. I got audio and video.
Why this? please help

thanks much

[Lotesdelere]

What is your OS ?
What is your source file ?
What is your output format ?

Please open Tools -> Messages (set Verbosity to 2) before you start the playback, and then paste the full resulting log here or on Pastebin.com or on Justpaste.it if it's too long.