I spoke to Eric yesterday evening (GMT) and he was going to email me about it, but he hasn't.

I have emailed a source file changed from one of your demo files that displays the issue.  If you run the file, click the edit link, then try to upload you should get the error.

If you change line 73 from

<asp:FormView ID="FormView1" DefaultMode="ReadOnly" runat="server">

to

<asp:FormView ID="FormView1" DefaultMode="Edit" runat="server">

it will then work, but not in the way I want. I need to be in readonly mode first.  It seems to be quite a subtle issue.

Can you try and repro your end please??