Hello and welcome to 4images forum.
It sounds like the problem is related to the upload file size limit set on the server (not 4images). Did you try upload very small image (5kb or so)? If small images accepted ok, then it confirms my guess. Llook in ACP (Admin Control Panel) -> phpinfo() and search for the following settings:
max_input_time
post_max_size
upload_max_filesize
upload_tmp_dir (this must have a valid path, with CHMOD 777)
if any of this settings are too low, contact your server's administrator and ask them to increase them.