The Q3 2012
release brought a major improvement in the databinding of RadHtmlChart and the price is a breaking change:
The DataField property of each series is now DataFieldY.
This is done to provide better databinding options for the rest of the series (e.g. Scatter and ScatterLine got a DataFieldX and Pie got NameField).
More information about the improvements and new features is available in
Q3 2012 Release Notes
New Features of RadHtmlChart for ASP.NET AJAX Ship a Month Ahead of Schedule