TextBox1.Text="" and alert(); not working inside update panel ,though database operation is working

.aspx page

----------------

<asp:ScriptManager ID="ScriptManager1" runat="server">
</asp:ScriptManager>
<asp:UpdatePanel ID="UpdatePanel1" runat="server">

<ContentTemplate>
<div>
<h1>Pick Up Management</h1>
<div><!-- asp.net inside-->
<div style="display:none ;">
<asp:HiddenField ID="cno" runat="server" />
<asp:Button ID="Button6" runat="server" Text="Do Not Click"
onclick="Button6_Click" />

<asp:HiddenField ID="pno" runat="server" />
<asp:Button ID="Button7" runat="server" Text="Do Not Click"
onclick="Button7_Click" style="width: 109px" />
<asp:HiddenField ID="cno2" runat="server" />
<asp:Button ID="Button8" runat="server" Text="Do Not Click"
onclick="Button8_Click" style="width: 109px"
/>
</div>

<table>
<tbody>

<tr>
<td class="style1">Search Customer</td>
<td></td>
<td></td>
<td></td>
</tr>

<tr>
<td>Customer No</td>
<td><asp:TextBox ID="TextBox15" runat="server"></asp:TextBox></td>
<td>Mobile No</td>
<td><asp:TextBox ID="TextBox16" runat="server"></asp:TextBox></td>
</tr>

<tr>
<td><asp:Button ID="Button1" class="button" runat="server" Text="Search" Width="110px"
onclick="Button1_Click" /></td>
<td></td>
<td></td>
<td></td>
</tr>

</tbody>
</table>
<div>
<asp:GridView ID="GridView1" runat="server">
<Columns>
<asp:TemplateField >
<ItemTemplate >
<asp:HyperLink ID="HyperLink1" runat="server" onclick='<%# Eval("customerno", "return getvalue(\"{0}\");")%>' Text="Select" ></asp:HyperLink>
</ItemTemplate>
</asp:TemplateField>
</Columns>
</asp:GridView>
</div>

<table>
<tbody border="1">
<tr>
<td class="style1">Personal Information</td>
<td></td>
<td class="style1">Contact Details</td>
<td></td>
</tr>

<tr>
<td>Customer No</td>
<td><asp:TextBox ID="TextBox1" runat="server"></asp:TextBox></td>
<td>Flat No</td>
<td><asp:TextBox ID="TextBox8" runat="server"></asp:TextBox></td>
</tr>

<tr>
<td>First Name</td>
<td><asp:TextBox ID="TextBox2" runat="server"></asp:TextBox></td>
<td>Wing</td>
<td><asp:TextBox ID="TextBox9" runat="server"></asp:TextBox></td>
</tr>

<tr>
<td>Middle Name</td>
<td> <asp:TextBox ID="TextBox3" runat="server"></asp:TextBox></td>
<td>Society</td>
<td><asp:TextBox ID="TextBox10" runat="server"></asp:TextBox></td>
</tr>

<tr>
<td>Last Name</td>
<td><asp:TextBox ID="TextBox4" runat="server"></asp:TextBox></td>
<td>LandMark</td>
<td><asp:TextBox ID="TextBox11" runat="server"></asp:TextBox></td>
</tr>

<tr>
<td>Gender</td>
<td><asp:DropDownList ID="DropDownList1" runat="server" Width="158px"
DataSourceID="SqlDataSource2" DataTextField="gender" DataValueField="gender"
Height="30px">
</asp:DropDownList>
<asp:SqlDataSource ID="SqlDataSource2" runat="server"
ConnectionString="<%$ ConnectionStrings:ConnectionString %>"
SelectCommand="SELECT [gender] FROM [gender]"></asp:SqlDataSource>
</td>
<td>Road</td>
<td><asp:TextBox ID="TextBox12" runat="server"></asp:TextBox></td>
</tr>

<tr>
<td>Contact Info</td>
<td></td>
<td>City</td>
<td><asp:TextBox ID="TextBox13" runat="server"></asp:TextBox></td>
</tr>

<tr>
<td>Email Add</td>
<td><asp:TextBox ID="TextBox5" runat="server"></asp:TextBox></td>
<td>Pincode</td>
<td><asp:TextBox ID="TextBox14" runat="server"></asp:TextBox></td>
</tr>

<tr>
<td>Mobile No 1</td>
<td><asp:TextBox ID="TextBox6" runat="server"></asp:TextBox></td>
<td></td>
<td></td>
</tr>

<tr>
<td>Mobile No 2</td>
<td><asp:TextBox ID="TextBox7" runat="server"></asp:TextBox></td>
<td></td>
<td></td>
</tr>

</tbody>
</table>

<table border="1">
<tbody>

<tr>
<td class="style1">Pick Up Info</td>
<td></td>
<td></td>
<td></td>
</tr>

<tr>
<td>Pick Up No</td>
<td><asp:TextBox ID="TextBox17" runat="server"></asp:TextBox></td>
<td>Notes</td>
<td><asp:TextBox ID="TextBox18" runat="server" TextMode="MultiLine"></asp:TextBox></td>
</tr>

<tr>
<td>Pick Up Time</td>
<td> <asp:TextBox ID="txt1" runat="server" class = "Calender" />
<img src="dtp/calender.png" />
</td>
<td></td>
<td></td>
</tr>

<tr>
<td>Pick Up Status</td>
<td><asp:DropDownList ID="DropDownList2" runat="server"
DataSourceID="SqlDataSource1" DataTextField="pickupstatus"
DataValueField="pickupstatus" Width="158px" Height="30px">
</asp:DropDownList>
<asp:SqlDataSource ID="SqlDataSource1" runat="server"
ConnectionString="<%$ ConnectionStrings:ConnectionString %>"
SelectCommand="SELECT [pickupstatus] FROM [pickupstatus]">
</asp:SqlDataSource>
</td>
<td></td>
<td></td>
</tr>

<tr>
<td><asp:Button ID="Button3" Height="30px" runat="server" Text="Add Pick Up"
onclick="Button3_Click" /></td>
<td><asp:Button ID="Button4" runat="server" Text="Update Pick Up"
onclick="Button4_Click" Visible="False" /></td>
<td><asp:Button ID="Button5" runat="server" Text="Delete Pick Up" Visible="False" /></td>
<td><asp:Button ID="Button9" class="button" runat="server" Text="Print Receipt"
onclick="Button9_Click" /></td>
</tr>

<tr>
<td>Generate Pick Up List </td>
<td></td>
<td></td>
<td></td>
</tr>

<tr>
<td>Mobile No </td>
<td><asp:TextBox ID="TextBox19" runat="server"></asp:TextBox></td>
<td>Pick Up Number</td>
<td><asp:TextBox ID="TextBox20" runat="server"></asp:TextBox></td>
</tr>

<tr>
<td>Customer No</td>
<td><asp:TextBox ID="TextBox21" runat="server"></asp:TextBox></td>
<td></td>
<td></td>
</tr>

<tr>
<td><asp:Button ID="Button2" class="button" runat="server" Text="Search Pick Up"
onclick="Button2_Click" /></td>
<td></td>
<td></td>
<td></td>
</tr>

</tbody>
</table>

<div>
<asp:GridView ID="GridView2" runat="server">
<Columns>
<asp:TemplateField >
<ItemTemplate >
<asp:HyperLink ID="HyperLink2" runat="server" onclick='<%# Eval("pickupno", "return getvalue2(\"{0}\");")%>' Text="Select" ></asp:HyperLink>
</ItemTemplate>
</asp:TemplateField>
</Columns>

</asp:GridView>
</div>

</div><!--asp.net div tag-->

</div>
</ContentTemplate>
</asp:UpdatePanel>
</form>

-----------------------------------.cs page button click

//add pick up entry
/////////////////insertion of data///////////
SqlConnection con2 = new SqlConnection();
SqlCommand cmd2 = new SqlCommand();
con2.ConnectionString = @"Data Source=.\SQLEXPRESS;AttachDbFilename=|DataDirectory|\Database1.mdf;Integrated Security=True;User Instance=True";
//Response.Write(con);
cmd2.Connection = con2;
con2.Open();
cmd2.CommandText = "Insert into pickup values(@customerno,@pickupno,@pickuptime,@pickupstatus,@pickupnotes,@customerm1,@customerm2)";
cmd2.Parameters.AddWithValue("@customerno", TextBox1.Text);
cmd2.Parameters.AddWithValue("@pickupno", TextBox17.Text);
String s = txt1.Text;
// String ss= s.Replace("/", "-");
//2012/11/25 12:23
//DateTime dt = DateTime.ParseExact(s, "yyyy/mm/dd hh:mm", CultureInfo.InvariantCulture);
DateTime dt = DateTime.Parse(s);
cmd2.Parameters.AddWithValue("@pickuptime", dt);
cmd2.Parameters.AddWithValue("@pickupstatus", DropDownList2.Text);
cmd2.Parameters.AddWithValue("@pickupnotes", TextBox18.Text);
cmd2.Parameters.AddWithValue("@customerm1", TextBox6.Text);
cmd2.Parameters.AddWithValue("@customerm2", TextBox7.Text);
cmd2.ExecuteNonQuery();
Response.Write("ok PickUp added");
TextBox1.Text = "";
TextBox2.Text = "";
TextBox3.Text = "";
TextBox4.Text = "";
TextBox5.Text = "";
TextBox6.Text = "";
TextBox7.Text = "";
TextBox8.Text = "";
TextBox9.Text = "";
TextBox10.Text = "";
TextBox11.Text = "";
TextBox12.Text = "";
TextBox13.Text = "";
TextBox14.Text = "";

TextBox17.Text = "";
TextBox18.Text = "";
txt1.Text = "";
//increasing the counter customerc in counters table
/////////////////updation of counter///////////
SqlConnection con7 = new SqlConnection();
SqlCommand cmd7 = new SqlCommand();
con7.ConnectionString = @"Data Source=.\SQLEXPRESS;AttachDbFilename=|DataDirectory|\Database1.mdf;Integrated Security=True;User Instance=True";
//Response.Write(con);
cmd7.Connection = con7;
con7.Open();
cmd7.CommandText = "Update counters set pickupc = pickupc + 1";
cmd7.ExecuteNonQuery();
//Response.Write("ok Pickup Counter updated");
//this one changed later
Button3.Enabled = false;
string showHelloWorld = "alert('Hello World');";

ScriptManager.RegisterClientScriptBlock(this, this.GetType(), "msg", showHelloWorld, true);