This is post which has a small trick for you about CQWP. If you arer uisng one and want to restore it to it's previous state, here is how you can do this using SharePoint designer.

1.Go to site/All Files/Style Library/XSL Style Sheets in SharePoint Designer 2010,







2.Right-click the ContentQueryMain.xsl>click Version History




3.If there are more than 1 versions, chances are that there is some code in there that causes this error, try to restore it.