[HttpException (0x80004005): A page can have only one server-side Form

Saudações,

Meu nome é Hugo,

Estou iniciando em Asp.net C# e estou tentando apenas permitir acesso a determinadas páginas do sistema só para usuários logados. Porém minha tela de Login dá o erro acima. Abaixo consta o erro por completo. Desde já agrade a ajuda de todos. Abraços, At+

Server Error in '/' Application. A page can have only one server-side Form tag.Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: System.Web.HttpException: A page can have only one server-side Form tag.

Source Error:

An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below. Stack Trace:

[HttpException (0x80004005): A page can have only one server-side Form tag.]
System.Web.UI.Page.OnFormRender() +85
System.Web.UI.HtmlControls.HtmlForm.RenderChildren(HtmlTextWriter writer) +36
System.Web.UI.HtmlControls.HtmlContainerControl.Render(HtmlTextWriter writer) +32
System.Web.UI.HtmlControls.HtmlForm.Render(HtmlTextWriter output) +204
System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter) +94
System.Web.UI.Control.RenderControl(HtmlTextWriter writer, ControlAdapter adapter) +210
System.Web.UI.Control.RenderControl(HtmlTextWriter writer) +106
System.Web.UI.HtmlControls.HtmlForm.RenderControl(HtmlTextWriter writer) +41
System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children) +183
System.Web.UI.Control.RenderChildren(HtmlTextWriter writer) +9
System.Web.UI.Control.Render(HtmlTextWriter writer) +10
System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter) +94
System.Web.UI.Control.RenderControl(HtmlTextWriter writer, ControlAdapter adapter) +210
System.Web.UI.Control.RenderControl(HtmlTextWriter writer) +106
System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children) +183
System.Web.UI.Control.RenderChildren(HtmlTextWriter writer) +9
System.Web.UI.HtmlControls.HtmlForm.RenderChildren(HtmlTextWriter writer) +173
System.Web.UI.HtmlControls.HtmlContainerControl.Render(HtmlTextWriter writer) +32
System.Web.UI.HtmlControls.HtmlForm.Render(HtmlTextWriter output) +204
System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter) +94
System.Web.UI.Control.RenderControl(HtmlTextWriter writer, ControlAdapter adapter) +210
System.Web.UI.Control.RenderControl(HtmlTextWriter writer) +106
System.Web.UI.HtmlControls.HtmlForm.RenderControl(HtmlTextWriter writer) +41
System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children) +183
System.Web.UI.Control.RenderChildren(HtmlTextWriter writer) +9
System.Web.UI.Control.Render(HtmlTextWriter writer) +10
System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter) +94
System.Web.UI.Control.RenderControl(HtmlTextWriter writer, ControlAdapter adapter) +210
System.Web.UI.Control.RenderControl(HtmlTextWriter writer) +106
System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children) +183
System.Web.UI.Control.RenderChildren(HtmlTextWriter writer) +9
System.Web.UI.Control.Render(HtmlTextWriter writer) +10
System.Web.UI.Page.Render(HtmlTextWriter writer) +107
System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter) +94
System.Web.UI.Control.RenderControl(HtmlTextWriter writer, ControlAdapter adapter) +210
System.Web.UI.Control.RenderControl(HtmlTextWriter writer) +106
System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +4087

Version Information: Microsoft .NET Framework Version:4.0.30319; ASP.NET Version:4.0.30319.18067