I got some emails saying System.Data.DataSet will throw a StackOverflowException. I tried several databases and tables, but I never got this error. Now, I found the difference: they are all using System.Guid.
I have already fixed this in the next version will be released this evening. There is a workaround available as a IAjaxObjectConverter. Download the GuidConverter.cs  and add the converter in your web.config file (i.e. <add type="CSharpSample.GuidConverter, YourAssemblyName"/>).