Ajax Control Tool Kit(3.0)& asp.net(3.5) Problrm Getting Exception

Question

 I have a problem
 When i <b>was using Ajax Control Tool Kit 1.0</b> that time i was getting no source code available further ...... that kind of error was comming.

But now I <b>changed my Ajax Control Tool kit to 3.0</b> now i am getting exception
<b>Description:</b>
 "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."
<b>Exception Details:</b>
System.Web.HttpException: Multiple controls with the same ID '_header' were found. FindControl requires that controls have unique IDs.
<b>Stack Trace:</b>
<pre lang="vb">[HttpException (0x80004005): Multiple controls with the same ID '_header' were found. FindControl requires that controls have unique IDs.]
   System.Web.UI.Control.FillNamedControlsTable(Control namingContainer, ControlCollection controls) +273
   System.Web.UI.Control.FillNamedControlsTable(Control namingContainer, ControlCollection controls) +320
   System.Web.UI.Control.FillNamedControlsTable(Control namingContainer, ControlCollection controls) +320
   System.Web.UI.Control.FillNamedControlsTable(Control namingContainer, ControlCollection controls) +320
   System.Web.UI.Control.FillNamedControlsTable(Control namingContainer, ControlCollection controls) +320
   System.Web.UI.Control.FillNamedControlsTable(Control namingContainer, ControlCollection controls) +320
   System.Web.UI.Control.EnsureNamedControlsTable() +61
   System.Web.UI.Control.FindControl(String id, Int32 pathOffset) +222
   System.Web.UI.Control.FindControl(String id, Int32 pathOffset) +255
   System.Web.UI.Control.FindControl(String id) +12
   AjaxControlToolkit.ExtenderControlBase.FindControlHelper(String id) in C:\Users\swalther\Projects\AspNetAjax\Releases\30930\AjaxControlToolkitSource\AjaxControlToolkit\ExtenderBase\ExtenderControlBase.cs:181
   AjaxControlToolkit.ExtenderControlBase.FindControl(String id) in C:\Users\swalther\Projects\AspNetAjax\Releases\30930\AjaxControlToolkitSource\AjaxControlToolkit\ExtenderBase\ExtenderControlBase.cs:209
   System.Web.UI.ExtenderControl.RegisterWithScriptManager() +72
   System.Web.UI.ExtenderControl.OnPreRender(EventArgs e) +19
   AjaxControlToolkit.ExtenderControlBase.OnPreRender(EventArgs e) in C:\Users\swalther\Projects\AspNetAjax\Releases\30930\AjaxControlToolkitSource\AjaxControlToolkit\ExtenderBase\ExtenderControlBase.cs:367
   System.Web.UI.Control.PreRenderRecursiveInternal() +80
   System.Web.UI.Control.PreRenderRecursiveInternal() +171
   System.Web.UI.Control.PreRenderRecursiveInternal() +171
   System.Web.UI.Control.PreRenderRecursiveInternal() +171
   System.Web.UI.Control.PreRenderRecursiveInternal() +171
   System.Web.UI.Control.PreRenderRecursiveInternal() +171
   System.Web.UI.Control.PreRenderRecursiveInternal() +171
   System.Web.UI.WebControls.WebParts.WebPart.PreRenderRecursiveInternal() +42
   System.Web.UI.Control.PreRenderRecursiveInternal() +171
   System.Web.UI.Control.PreRenderRecursiveInternal() +171
   System.Web.UI.Control.PreRenderRecursiveInternal() +171
   System.Web.UI.Control.PreRenderRecursiveInternal() +171
   System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +842</pre>

Please send some solution on this problem I am searching for almost 2 days for it.
Thanks.