Hey there Hemmi - I made the unofficial batch upload mod of AKOGallery.
I've heard of quite a few instances where servers will timeout with larger batches - that will vary from server to server, but I personally have been able to upload over 100 images at a time. Unfortunately, there's not much to do about this except to just to do smaller batches...
Also, I did have one instance where a user was saving his .jpg files with some extra file information (author, caption, description, date, etc.) and GD wasn't wanting to open them for processing - that resulted in the error that you are reporting. I opened up the photos in ImageReady and re-saved them and then they processed fine.
Also, I just noticed that in the error message from your post that the generated filename doesn't have an extension (.jpg or .png - i think thats what GD supports). Did your source file have an extension on it? If not, that would definately mess it up.