i think that due to the improper close of the tags (asp controls) this issue might have raised.
i changed the code a bit and it worked fine for me. Check it out
<label>
Area(in Sq Ft)
<asp:RequiredFieldValidator ID="RequiredFieldValidator1" runat="server" ControlToValidate="Txtarea"
ValidationGroup="1"> <img alt="" src='<%=ResolveClientUrl("~/Images/erroricon.png")%>' /> </asp:RequiredFieldValidator>
<asp:TextBox ID="Txtarea" runat="server"></asp:TextBox>
<br />
Region
<asp:TextBox ID="Txtregion" runat="server"></asp:TextBox>
Name
<span>
<asp:RequiredFieldValidator ID="RequiredFieldValidator2" runat="server" ControlToValidate="TxtName"
ErrorMessage="Enter Your Name" ValidationGroup="1"> <img alt="" src='<%=ResolveClientUrl("~/Images/erroricon.png")%>' /></asp:RequiredFieldValidator>
<asp:TextBox ID="TxtName" runat="server"></asp:TextBox>
Mobile No.
<asp:TextBox ID="txtmobile" runat="server"></asp:TextBox>
<asp:RegularExpressionValidator ID="RegularExpressionValidator1" runat="server" ValidationExpression="^[0-9]{10}"
ControlToValidate="txtmobile" ErrorMessage="Incorrect Number" ValidationGroup="1">
<img alt="" src='<%=ResolveClientUrl("~/Images/erroricon.png")%>' /></asp:RegularExpressionValidator>
<br />
<div style="clear: both; padding-top: 22px;">
</div>
<asp:Button ID="Btnsave" runat="server" Text="Send" Width="78px" Style="color: #fff;
font-size: 12px; line-height: 15px; background: url(../images/button-1.jpg) 0 0 repeat-x #08489f;
border-top: #339ed3 1px solid; border-right: #2881c3 1px solid; border-bottom: #1a62b1 1px solid;
border-left: #2881c3 1px solid; display: inline-block; text-decoration: none;
padding: 5px 21px 7px 19px; cursor: pointer;" ValidationGroup="1" />
<asp:Label ID="Label1" runat="server" ForeColor="Black"></asp:Label>
</span>
</label>