I was running into trouble when using the out-of-the-box RSS Feed Web Part of SharePoint 2010 on a publishing page. Especially when the Web Part wasn’t configured with a RSS feed, because it shows the following message:
Not much help in this error. A work-around would be to set the publishing page in Edit mode, and than click the “Open the tool pane” link. Not very user friendly.
I included the ie55up.js in the Master Page using the <SharePoint:ScriptLink> and it solved the problem.