From javadch on discussion
"I have a list of people based on your sample code. when list is rendered and I have grouped in based on one column, and try to add second one, the following error occurs!
"Sequence contains more than one matching element"
would you please let me know what is the problem.
I have traced the source code, every thing is fine with ApplyGrouping, but at the execution time it does not get run on the data."