Is this the same file that you had trouble uploading to s3 in your previous post?
It's hard to be sure with only the top of the stack trace, but it looks like there's a disagreement between youtube, your local class2go database, and the contents of your s3 storage. As currently written, when AWS credentials are set, class2go tries to upload videos to a bucket on s3 in addition to sending them to youtube. Then, when it needs information about the video (like the file size, which is referred to in the screenshot you attached), it queries s3 to find that information out. But if the file hasn't been uploaded to s3 (because there was some error during upload, for example) then it won't be able to complete the query, and an error results.
I think that if you resolve your problem with S3 uploading (for example, by putting the file in the appropriate bucket from the web console) then this problem will go away.
I noticed on the other thread that you wanted to use something besides s3 for cloud storage. If you get that working, you could try deleting this video from class2go and re-uploading it. If storages is smart enough, that may make this error go away. Please let us know how it goes.
Joe