GridView acionou o evento RowEditing, que não foi tratado.

<asp:GridView ID="grdDescicao" runat="server" AutoGenerateColumns="False" Width="100%" 
            BackColor="White" AllowPaging="True" BorderColor="#3366CC" 
            BorderStyle="None" BorderWidth="1px" 
            CellPadding="4" 
            onrowcommand="grdDescicao_RowCommand" 
            DataKeyNames="UGE,AnoBase,Sequencia,CNPJ/CPF" AllowSorting="True" 
            onpageindexchanging="grdDescicao_PageIndexChanging" >
            <PagerSettings FirstPageText="Primeiro" LastPageText="Ultimo" Mode="NumericFirstLast" NextPageText="Proxímo" PreviousPageText="Anterior" />
            <RowStyle BackColor="White" ForeColor="#003399" />
            <Columns >
            <asp:BoundField DataField="Tipo Sancao" HeaderText="Tipo Sanção" ItemStyle-Width="110px">
                <ItemStyle Width="110px"></ItemStyle>
            </asp:BoundField>
	        <asp:BoundField DataField="Orgao" HeaderText="Orgão" />
	        <asp:BoundField DataField="Processo" HeaderText="Processo" />
            <asp:BoundField DataField="Inicio" HeaderText="Início" 
                DataFormatString="{0:dd/MM/yyyy}" HtmlEncode="false" ItemStyle-Width="50px">
<ItemStyle Width="50px"></ItemStyle>
            </asp:BoundField>
	        <asp:BoundField DataField="Termino" HeaderText="Término" 
                DataFormatString="{0:dd/MM/yyyy}" HtmlEncode="false" ItemStyle-Width="50px">
<ItemStyle Width="50px"></ItemStyle>
            </asp:BoundField>
	        <asp:BoundField DataField="Poder" HeaderText="Poder" Visible="false"/>
	        <asp:BoundField DataField="Codigo UGE" HeaderText="Codigo UGE" Visible="false"/>
	        <asp:BoundField DataField="UGE" HeaderText="U.G.E." Visible="false"/>
	        <asp:BoundField DataField="Codigo UGO" HeaderText="Codigo UGO" Visible="false"/>
	        <asp:BoundField DataField="UGO" HeaderText="U.G.O." Visible="false"/>
	        <asp:BoundField DataField="Fundamento Legal" HeaderText="Fundamento Legal" Visible="false"/>
	        <asp:BoundField DataField="Prazo" HeaderText="Prazo" Visible="false"/>
            <asp:ButtonField CommandName="Edit" HeaderText="Link" Text="Visualizar">
            <ItemStyle Width="10px" />
            </asp:ButtonField>
        </Columns>
            <SelectedRowStyle BackColor="#009999" Font-Bold="True" ForeColor="#CCFF99" />
            <HeaderStyle BackColor="#003399" Font-Bold="True" ForeColor="#CCCCFF" />
        </asp:GridView>

protected void grdDescicao_RowCommand(object sender, GridViewCommandEventArgs e)
        {
            if (e.CommandName.Contains("Edit"))
            {
                string UGE = grdDescicao.DataKeys[Convert.ToInt32(e.CommandArgument)]["UGE"].ToString();
                string AnoBase = grdDescicao.DataKeys[Convert.ToInt32(e.CommandArgument)]["AnoBase"].ToString();
                string Sequencia = grdDescicao.DataKeys[Convert.ToInt32(e.CommandArgument)]["Sequencia"].ToString();
                string CNPJCPF = grdDescicao.DataKeys[Convert.ToInt32(e.CommandArgument)]["CNPJ/CPF"].ToString();

                BS_ConsultaPublicaDescisao bs = new BS_ConsultaPublicaDescisao();
                PreencherCampos(bs.CarregarDetalhes(UGE, AnoBase, Sequencia, CNPJCPF));
            }  
        }

        protected void grdDescicao_PageIndexChanging(object sender, GridViewPageEventArgs e)
        {
            grdDescicao.PageIndex = e.NewPageIndex;
            CarregarGridOutrasSancoes();
        }
private void CarregarGridOutrasSancoes()
        {
            string CNPJCPF = HttpContext.Current.Items["CNPJCPF"].ToString();

            BS_ConsultaPublicaDescisao bs = new BS_ConsultaPublicaDescisao();
            DataSet ds = bs.CarregarGrid(CNPJCPF, null, null, null);

            grdDescicao.DataSource = ds;
            grdDescicao.DataBind();
        }