User288213138 posted
Hi jsshivalik,
I tried to reproduce your problem, but I found it worked.What's error in you code?
This is my code:
<div class="modal fade" id="myModal" role="dialog">
<div class="modal-dialog" style="width: 360px;">
<div class="modal-content">
<div class="modal-header" style="background-color: #337AB7; padding: 16px 16px; color: #FFF; border-bottom: 2px dashed #337AB7;">
<h4 class="modal-title"></h4>
</div>
<div class="modal-body">
<asp:TextBox CssClass="form-control" ID="txtRemarks" TextMode="MultiLine" Rows="5" runat="server"></asp:TextBox>
<asp:RegularExpressionValidator Display="Dynamic" ControlToValidate="txtRemarks" ID="rfv0" ValidationExpression="^[A-Za-z0-9]{5}$" runat="server" ErrorMessage="Minimum 5 characters required.">
</asp:RegularExpressionValidator>
</div>
<div class="modal-footer">
<asp:Button ID="Button1" runat="server" Text="Save" OnClick="Button1_Click" />
</div>
</div>
</div>
</div>
Aspx.cs:
protected void Button1_Click(object sender, EventArgs e)
{
Response.Write(txtRemarks.Text);
}
The result:

If you haven't solved the problem, please post your code behind.
Best regards,
Sam