I've got an Assets field in a Matrix. I can upload to S3 and Local upload directories while in the CP. When I try to upload to either S3 or local directories in my Channel Form page, I get the following error message:
"Could not upload the file - server returned an unexpected response. Please check the server settings".
If I replace the Assets field with a EE File fieldtype, it works fine, but we'd prefer to be using S3, hence the love for Assets.
*I haven't tried just a stand alone Assets field instead of a field in a matrix, but I don't think that will fix the problem.