I've created a publishing page, placed a custom web part on in and published it. When I try to navigate to it I see this text instead of the content:

Page Content field value. Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.

Searching the web I've found similar pages, for example: http://www.diwug.nl/Pages/default.aspx?id=participants

One thing about the page is that it's getting a query parameter called id - could that be causing the error?