I have limited the file size of pictures attached to posts. You will need to resize them. If unlimited file sizes were allowed the database would get to be unmanageable. For most web viewing a 640x480 file that is about 100k in size will be more than sufficient.
You are allowed to post up to 5 pics per post with a max size of 1MB. That means 1 pic that is 1MB in size or 5 pics that add up to 1MB. Anything over that and the software will reject it.