This documents errors you're likely to see with Kupu.

"Couldn't set design mode. Kupu will not work with this	browser"

  This occurs when the contents of the main <iframe> ends up being
  something that doesn't smell like html. This could be because it
  actually isn't html, or because it is being served with the wrong
  content type.

"no cleanup expressions configured"

  This happens when the cleanup tool doesn't find any expressions in
  the xml config block. It can be cured by either removing the cleanup
  tool or inserting the sample expressions from the top of
  kupucleanupexpressions.js into the <kupuconfig> xml block at the top
  of your editing template.

"Error loading kupudrawers/drawel.xsl:404"

  This applies to any .xsl or .js file that returns a 404. It means
  that the urls inside your editing template aren't being correctly
  generated. View the source of your editing template, check where the
  urls are pointing andadjust them so they actually find the right thing.