AJAX PageRequestManagerParserErrorException error in asp.net page

Many issues can cause that error. It's usually a Response.Write call, but anything that modifies the response can cause it.

We probably won't be able to help you unless you post some pertinent code-behind.

I had a similar problem in the past trying to stream an excel document with a button inside an update panel. Here is my solution, hope it helps.

VB.NET:

Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load

    Dim sm = ScriptManager.GetCurrent(Me.Page)
    sm.RegisterPostBackControl(Me.YOUR_BUTTON)

    AddPostBackTrigger(Me.YOUR_BUTTON.UniqueID.ToString())

End Sub


Public Sub AddPostBackTrigger(ByVal ControlId As String)
    Dim existingTrigger = FindPostBackTrigger(ControlId)
    If existingTrigger Is Nothing Then
        Dim trigger As New PostBackTrigger()
        trigger.ControlID = ControlId
        Me.YOUR_UPDATE_PANEL_GOES_HERE.Triggers.Add(trigger)
    End If
End Sub
Public Sub RemovePostBackTrigger(ByVal ControlId As String)
    Dim existingTrigger = FindPostBackTrigger(ControlId)
    If existingTrigger IsNot Nothing Then
        Me.YOUR_UPDATE_PANEL_GOES_HERE.Triggers.Remove(existingTrigger)
    End If
End Sub
Private Function FindPostBackTrigger(ByVal ControlId As String) As PostBackTrigger
    For Each Trigger In Me.YOUR_UPDATE_PANEL_GOES_HERE.Triggers
        If Trigger.GetType().Name = "PostBackTrigger" Then
            Dim pt = CType(Trigger, PostBackTrigger)
            If pt.ControlID = ControlId Then
                Return pt
            End If
        End If
    Next
    Return Nothing
End Function

C#:

protected void Page_Load(object sender, EventArgs e)
{
    ScriptManager sm = ScriptManager.GetCurrent(Page);
    if (sm != null) sm.RegisterPostBackControl(YOUR_CONTROL);
    AddPostBackTrigger(YOUR_CONTROL.UniqueID);
}

private void AddPostBackTrigger(string controlId)
{
    PostBackTrigger existingTrigger = FindPostBackTrigger(controlId);

    if (existingTrigger != null)
    {
        var trigger = new PostBackTrigger {ControlID = controlId};
        YOUR_UPDATE_PANEL.Triggers.Add(trigger);
    }
}

private PostBackTrigger FindPostBackTrigger(string controlId)
{
    return
        YOUR_UPDATE_PANEL
            .Triggers.OfType<PostBackTrigger>()
            .FirstOrDefault(pt => pt.ControlID == controlId);
}