Forms Data Controls :: Bind Value From DataItem?

I've bound a IeNumerable<class> to a repeater.On the repeater i've got a ItemDataBound.Right there i want the value of 1 of the items in my string s.So i've build this code.But if i run it i get this error:

System.Web.HttpException: DataBinding: 'dftv.AutoDiskClass+Merk' does not contain a property with the name 'nMerkID'.

if i run it again and put a breakpoint at this row, and push the DataItem, i get this information.
But how can i get the value of nMerkID in my string?The class i put in it is:

public class Merk
{
public string nMerkID = "";
public string Merknaam = "";
}