I tried again and got the same error message.
Then I tried shortening the post and having just the one embedded photo and it worked
I think the problem is the time it takes for long posts to be posted. You can try setting "Use a persistent connection" under the server settings core configuration. That should keep the server connection active to increase performance. On the other hand, nobody else had a problem so just ignore me and do nothing
Even though the photos are 1600x1200 they are embedded with [
img width=800]<picture URL>[/
img] so the displayed size is 800 pixels wide.