Try posting just one. It could be that the process times out trying to post all four. Nothing to do with the 4 mb limit of LuLa, but the server's timing limits. *
* EDIT: Just found an explanation from the site administrator:
With the timeouts it's because of the upload speed of your internet connection and the timeout that your browser defaults to (which I don't think you can change). You should still be able to upload larger images (up to 4MB), but try them one at a time if you get timeouts on the browser end of things. It only allows a connection to happen for so long before your browser decides it's been too long and stops things...