What fails a facebook picture upload?

Answer 1

In most of the cases is the server load facebook is facing generates the upload problems.

The HTML uploader has to transfer the whole content to the server before resizing it, in most of the cases the connection drops before the image is uploaded.

The Java Uploader is better, it resizes the photo before uploading so it is more reliable.

Third party applications are even more immune to problems, since they are using a limited API on the facebook, most of the time only the photo upload API. They are, generally speaking :), treating errors better than the Java interface and automatically doing more retries.

When encountering problems with facebook photo uploads, you can try a different upload method. I personally use AZImage (see links), because it has a better image quality that the Java interface and is more stable and faster than both upload methods.