Hi Dario,
We have seen a similar error as well with our custom footer. The root cause is likely because in HTML the img tag does not have to be closed, but in XHTML - which requires well-formed XML - would require the closing tag (or self-closing tag). We changed the <img ...> tags in our custom footer into <img .../> and that fixed the problem.
But your message seems to indicate that the issue is with the fixed footer and I do not know how to change that, except by changing the xhtml in the deployed war.
regards,
Kris