SelectionList postback problems

I am binding a table to a selectionlist on a mobile site I am building, but it doesn't seem to want to grab the users selection. I get a "Object reference not set to an instance of an object" error.
This here is a Panel with the selection list which is being bound from the code behind, and the command/submit button.
 
<mob:Panel ID="pnl_tab3" runat="server" Visible="false"> <mob:Label ID="lbl_errorMsg1" runat="server" /> <mob:SelectionList ID="rpt_select" runat="server" SelectType="Radio" /> <mob:Command ID="cmd_select" runat="server" Text="select" OnItemCommand="lkBtn" /> <mob:Command ID="btnN3" runat="server" Text="Next" OnItemCommand="nextBtn" CommandArgument="3" Visible="false" /> </mob:Panel> And this is a sumarized version of the code behind:
protected void Page_Load(object se ...