Resolume Forum

to recreate:

drag a file with audio and video to resolume,
delete the video stream from the clip
save composition
delete the thumbnail file,
reload composition, - the wave data gets generated, - containing only the audio data, no video thumbnail.
now drag the same file into resolume: only the audio stream is present on the new clip.

I love the amount of hoops you jumped through to get there though..

yes, me too:).

this can also happen if you are moving your composition and files to a new machine and decide to use the video stream from a file that exists in your composition as audio only.

so for anyone running into this, you can get around by finding, and deleting the thumbnail file and importing the clip to a blank composition first.
The thumbnail files are located:

• Mac: /Users/[username]/Library/Application Support/Resolume Avenue 4/
  PC: C:\Documents and Settings\[username]\Application Data\Resolume Avenue 4\
  Win7: C:\Users\[username]\AppData\Roaming\Resolume Avenue 4\

For Arena replace the Avenue with Arena in the path,
the thumbnail file name starts with your original file name.

then you can open up your destination comp, and use import the file as always.