list box bound to dataset

I have a list box bound to a dataset filled by a sqldataadapter. I get an error when I try to acquire the selectedvalue from the list box in code. The values seen turn to all the same value: system.data.datarowview
I don't get this error when I bind the listbox to an array.
Anyone know a reason why this happens?

dim g as string
g = listbox.selectedvalue

thanks