I suspect the problem is not with the fact that you've created a runtime version, but simply that the pathname to the video clip is not valid for their location. Are you saying that a runtime version of your file running on your own desktop in the same location as the original file (unlikely) produces the error message?
How did you link the video clip to the file?
You were right. The video clips were in a different folder. I resolved the problem by moving the application and runtime document file into the same folder as the video clips folder. Is seems to be working fine now.
Thanks for your help.