Well Windell, it's just a case of normal use of ETP: I click on the "Edit this page" link at the bottom right of the page, and then click on the link to edit the content attribute. When I add
img src="/storage/download/sequencing.jpg?version_id=146982" width="1067" height="1436" border="0" [within tags]
(plus a paragraph of text) and submit the page I get the error described above.
It seems that it is the image (150 Kb) that causes the trouble, because when I follow the same procedure, but without actually editing the content or just adding a piece of text, I can submit the page.
Thanks!