R – Label not becoming visible inside of repeater inside an updatepanel

I have an UpdatePanel that contains a Repeater. in the ItemTemplate of the repeater there is a button and a label.

When the button gets pressed, it performs some functionality, and then sets the label to visible and disables the button.

However none of the UI changes are being made to the webpage.

Here is the code, which when stepping through in debugger appears to work fine:

protected void CommentRepeater_ItemCommand(object source, RepeaterCommandEventArgs e)
{
    if (e.CommandName == "report")
    {
        (e.Item.FindControl("btnReportComment") as ImageButton).Enabled = false;
        Label thanksLabel = (Label)e.Item.FindControl("lblReportedComment");
        thanksLabel.Visible = true;
    }

    pnlCommentsUpdater.Update();
}

and the page's code (excluding code outside of the repeater)

<asp:UpdatePanel UpdateMode="Conditional" ID="pnlCommentsUpdater" runat="server">
    <ContentTemplate>
        <asp:LinkButton ID="lnkPhoto1Comments" runat="server" Text="0 Comments" OnClick="lnkPhoto1Comments_Click" CssClass="dark-gray regular bold"></asp:LinkButton>      
        <asp:Panel ID="pnlPhoto1Comments" runat="server" Visible="False">
        <asp:Repeater ID="Repeater1" runat="server" OnItemCommand="CommentRepeater_ItemCommand">
            <ItemTemplate>
                <br />
                <hr width="100%" size="1" color="#CCCCCC" />
                <table width="534" cellpadding="0" cellspacing="0" border="0">
                    <tr>
                        <td width="150" align="left" valign="top">
                            <span class="blue small bold"><%# Eval("PostedBy") %>,</span><br />
                            <span class="light-gray small bold"><%# Eval("DateCreated", "{0:g}") %></span>
                        </td>
                        <td width="20"></td>
                        <td width="252" align="left" valign="top">
                            <div STYLE="word-wrap:break-word;width:252px;left:0">
                                <span class="dark-gray small bold"><%# Eval("CommentText") %></span>
                            </div>
                        </td>
                        <td width="20"></td>
                        <td width="92" valign="bottom">
                            <asp:ImageButton ID="btnReportComment" runat="server" ImageUrl="../images/inappropriate_off.png" CssClass="domclickroll images/inappropriate_on.png images/inappropriate_on.png" AlternateText="Inappropriate" CommandName="report" CommandArgument='<%#Eval("CommentId") %>' /><br />
                            <asp:Label ID="lblReportedComment" runat="server" Visible="false" CssClass="Regular bold blue" Text="Thanks. We'll check it out!"></asp:Label>
                        </td>
                    </tr>
                </table>
            </ItemTemplate>
        </asp:Repeater>

As I said, the debugger shows it to be working fine, however it simply doesn ot show the label in the browser after clicking the button.

Anyone know what I'm doing wrong?

The error is: "Sys.WebForms.PageRequestManagerParserErrorException: The message received from the server could not be parsed. Common causes for this error are when the response is modified by calls to Response.Write(), response filters, HttpModules, or server trace is enabled."

And I am calling

ScriptManager.GetCurrent(Page).RegisterPostBackControl(Repeater1); 

in the page load, which I read in some sites is the solution, but it did not help.