We have problem with custom lightbox in dhtmlxScheduler because in your example you used the HTML controller. can we use server side controller in our custom lightbox By the way did you place custome form in side User Controller
<%@ Control Language="C#" AutoEventWireup="true" CodeBehind="uc_taskFrom.ascx.cs" Inherits="Compudata_ProjectManager.userController.uc_taskFrom" %>
<div>
<!-- begin of Content Create TaskForm -->
<!-- Script manager-->
<asp:ScriptManager ID="ScriptManager1" runat="server">
</asp:ScriptManager>
<!-- Validation Summary msg vs_TaskForm-->
<asp:ValidationSummary ID="vs_TaskForm" runat="server" ForeColor="#CC0000" />
<asp:UpdatePanel ID="UpdatePanel1" runat="server">
<ContentTemplate>
<!-- begin of Content Create TaskForm -->
<asp:Panel ID="Panel1" runat="server" GroupingText="Create New Task">
<table>
<tr>
<td>
<label>
Project:</label>
</td>
<td>
<asp:DropDownList ID="ddl_projectsList" runat="server" DataSourceID="SqlDataSourceProjectList"
DataTextField="projectName" DataValueField="projectID" AppendDataBoundItems="True"
OnSelectedIndexChanged="ddl_projectsList_SelectedIndexChanged" AutoPostBack="True">
<asp:ListItem Value="-1">Select Project</asp:ListItem>
</asp:DropDownList>
<asp:CompareValidator ID="cv_projectList" runat="server" ControlToValidate="ddl_projectsList"
ErrorMessage="Select Project" ForeColor="#FC0000" Operator="NotEqual" ValueToCompare="-1">*</asp:CompareValidator>
<asp:SqlDataSource ID="SqlDataSourceProjectList" runat="server" ConnectionString="<%$ ConnectionStrings:Compudata_ProjectManagerConnection %>"
SelectCommand="SELECT [projectID], [projectName] FROM [Projects] ORDER BY [projectName]">
</asp:SqlDataSource>
</td>
</tr>
<tr>
<td>
<label>
Task Name:</label><em>*</em>
</td>
<td>
<asp:TextBox ID="txtb_taskName" runat="server"></asp:TextBox>
<asp:RequiredFieldValidator ID="rfv_taskName" runat="server" ControlToValidate="txtb_taskName"
ErrorMessage="Enter Task Name" ForeColor="#F60000">*</asp:RequiredFieldValidator>
</td>
</tr>
<tr>
<td>
Default Tech:
</td>
<td>
<asp:Literal ID="lit_dafaultTech" runat="server"></asp:Literal>
</td>
</tr>
<tr>
<td>
<label>
Assigned To :</label><em>*</em>
</td>
<td>
<asp:DropDownList ID="ddl_usersList" runat="server" AppendDataBoundItems="True" DataSourceID="SqlDataSourceUserList"
DataTextField="UserName" DataValueField="UserId">
</asp:DropDownList>
<asp:RequiredFieldValidator ID="RequiredFieldValidator1" runat="server" ControlToValidate="ddl_usersList"
CssClass="Validator" ErrorMessage="select Tech" InitialValue="-1">*</asp:RequiredFieldValidator>
<asp:SqlDataSource ID="SqlDataSourceUserList" runat="server" ConnectionString="<%$ ConnectionStrings:Compudata_ProjectManagerConnection %>"
SelectCommand="SELECT [UserId], [UserName] FROM [vw_aspnet_Users]"></asp:SqlDataSource>
</td>
</tr>
<tr>
<td>
<label>
Status :</label><em>*</em>
</td>
<td>
<asp:DropDownList ID="ddl_status" runat="server" AppendDataBoundItems="True">
</asp:DropDownList>
<asp:RequiredFieldValidator ID="RequiredFieldValidator2" runat="server" ControlToValidate="ddl_status"
ErrorMessage="select Status" InitialValue="-1" CssClass="Validator">*</asp:RequiredFieldValidator>
<asp:SqlDataSource ID="status_sqlDS" runat="server" ConnectionString="<%$ ConnectionStrings:Compudata_ProjectManagerConnection %>"
SelectCommand="GetAllStatus" SelectCommandType="StoredProcedure"></asp:SqlDataSource>
</td>
</tr>
<tr>
<td>
<label>
Priorty:</label><em>*</em>
</td>
<td>
<asp:DropDownList ID="ddl_priority" runat="server" AppendDataBoundItems="True">
</asp:DropDownList>
<asp:RequiredFieldValidator ID="RequiredFieldValidator3" runat="server" ControlToValidate="ddl_priority"
ErrorMessage="Select one" CssClass="Validator" InitialValue="-1">*</asp:RequiredFieldValidator>
<asp:SqlDataSource ID="priority_sqlDC" runat="server" ConnectionString="<%$ ConnectionStrings:Compudata_ProjectManagerConnection %>"
SelectCommand="GetAllPriority" SelectCommandType="StoredProcedure"></asp:SqlDataSource>
</td>
</tr>
<tr>
<td>
<label>
Estimate Time eg(1.50):</label>
</td>
<td>
<asp:TextBox ID="txtb_estTime" runat="server" Style="direction: ltr"></asp:TextBox>
</td>
</tr>
<tr>
<td>
<label>
Description:</label><em>*</em>
</td>
<td>
<asp:TextBox ID="txtb_Description" runat="server" TextMode="MultiLine"
Width="600px" Height="300px"></asp:TextBox>
</td>
</tr>
<tr>
<td>
</td>
</tr>
<tr>
<td colspan="2">
<label>
Send Email:
</label>
<asp:CheckBox ID="ch_sendEmail" runat="server" Text="Send Email to assigned Tech"
Checked="True" />
</td>
</tr>
<tr>
<td>
<label>Start Date: </label>
</td>
<td>
<asp:TextBox ID="txtb_startDate" runat="server"></asp:TextBox>
</td>
</tr>
<tr>
<td>
<label>End Date: </label>
</td>
<td>
<asp:TextBox ID="txtb_endDate" runat="server" CssClass=".datetimepicker"></asp:TextBox>
</td>
</tr>
<tr>
<td>
<label>show on Calendar </label>
</td>
<td>
<asp:CheckBox ID="chb_calendar" runat="server" Text="show on Calendar"></asp:CheckBox>
</td>
</tr>
<tr>
<td>
<asp:Label ID="lblMessage" runat="server"></asp:Label>
</td>
<td>
<asp:Button ID="btn_createTask" runat="server" Text="Create Task" OnClick="createTask_Click" />
<asp:Button ID="Button2" runat="server" Text="Cancel" />
</td>
</tr>
</table>
<br />
<!-- begin of Web template option -->
<table class="style1">
<tr>
<td>
<asp:LinkButton ID="lnkb_clientRMA" runat="server"
onclick="lnkb_clientRMA_Click"
>CLIENT RMA RETURN</asp:LinkButton> </td>
<td>
<asp:LinkButton ID="lnkb_LG_SERVICE" runat="server"
onclick="lnkb_LG_SERVICE_Click">LG SERVICE</asp:LinkButton> </td>
<td>
<asp:LinkButton ID="lnkb_PHONE_REMOTESUPPORT" runat="server"
onclick="lnkb_PHONE_REMOTESUPPORT_Click">PHONE/REMOTE SUPPORT</asp:LinkButton> </td>
<td>
<asp:LinkButton ID="lnkb_SEAGATE_RMA_RETURN" runat="server"
onclick="lnkb_SEAGATE_RMA_RETURN_Click">SEAGATE RMA RETURN</asp:LinkButton> </td>
<td>
<asp:LinkButton ID="lnkb_ON_SITE_SERVICE" runat="server"
onclick="lnkb_ON_SITE_SERVICE_Click"> ON-SITE SERVICE</asp:LinkButton></td>
<td>
<asp:LinkButton ID="lnkb_ZEISS_RMA_DIAGNOSTIC" runat="server"
onclick="lnkb_ZEISS_RMA_DIAGNOSTIC_Click">ZEISS RMA AND DIAGNOSTIC</asp:LinkButton> </td>
</tr>
<tr>
<td>
<asp:LinkButton ID="lnkb_LENOVO_SERVICE" runat="server"
onclick="lnkb_LENOVO_SERVICE_Click">LENOVO SERVICE</asp:LinkButton></td>
<td>
<asp:LinkButton ID="lnkb_MONTHLY_SERVICE" runat="server"
onclick="lnkb_MONTHLY_SERVICE_Click">MONTHLY SERVICE</asp:LinkButton> </td>
<td>
<asp:LinkButton ID="lnkb_Power_Supply_RMA" runat="server"
onclick="lnkb_Power_Supply_RMA_Click">Power Supply RMA</asp:LinkButton></td>
<td>
<asp:LinkButton ID="lnkb_IN_SHOP_SERVICE" runat="server"
onclick="lnkb_IN_SHOP_SERVICE_Click" >IN-SHOP SERVICE</asp:LinkButton></td>
<td>
<asp:LinkButton ID="lnkb_VENDOR_RMA_RETURN" runat="server"
onclick="lnkb_VENDOR_RMA_RETURN_Click">VENDOR RMA RETURN</asp:LinkButton></td>
<td>
</td>
</tr>
</table>
<!-- end of Web template option -->
</asp:Panel>
<!-- end of Content Create TaskForm -->
</ContentTemplate>
<Triggers>
<asp:AsyncPostBackTrigger ControlID="ddl_projectsList" EventName="SelectedIndexChanged" />
</Triggers>
</asp:UpdatePanel>
</div>
you can place your web form in .aspx page and use this function this line will create iframe window