ASP.net error

post the upload.aspx back end code or excel connection function at least

If there is any 'If' condition OR 'switch' something like that you need to return the value in all conditions
In other words , the function need to return value in all of its condition. Surely in some condition it is missing - please check

Raj

In your ExcelConnection function you are not returning a valid value for the functions end points.  If the function is boolean you need to make sure you return a true or false, an integer returns an integer etc.

Sorry. Thought I had posted the code. Here iy is:
Imports System.Data.OleDb

Public Class WebForm1


    Inherits System.Web.UI.Page

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

    End Sub


    Protected Sub ButtonUpload_Click(ByVal sender As Object, ByVal e As EventArgs) Handles ButtonUpload.Click
        Try
            PanelUpload.Visible = True
            PanelView.Visible = False
            PanelImport.Visible = False
        Catch ex As Exception
            MsgBox(Err.Description)
        End Try

    End Sub

    Protected Sub ButtonUploadFile_Click(ByVal sender As Object, ByVal e As EventArgs) Handles ButtonUploadFile.Click
        If FileUploadExcel.HasFile Then
            Try
                ' alter path for your project
                FileUploadExcel.SaveAs(Server.MapPath("~/ExcelImport.xls"))
                LabelUpload.Text = "Upload File Name: " & _
                    FileUploadExcel.PostedFile.FileName & "<br>" & _
                    "Type: " & _
                    FileUploadExcel.PostedFile.ContentType & _
                    " File Size: " & _
                    FileUploadExcel.PostedFile.ContentLength & " kb<br>"
            Catch ex As Exception
                LabelUpload.Text = "Error: " & ex.Message.ToString
            End Try
        Else
            LabelUpload.Text = "Please select a file to upload."
        End If

    End Sub
    Protected Function ExcelConnection() As OleDbCommand
        Try
            ' Connect to the Excel Spreadsheet
            Dim xConnStr As String = "Provider=Microsoft.Jet.OLEDB.4.0;" & _
                  "Data Source=" & Server.MapPath("ExcelImport.xls") & ";" & _
                  "Extended Properties=Excel 8.0;"

            ' create your excel connection object using the connection string
            Dim objXConn As New OleDbConnection(xConnStr)
            objXConn.Open()
            ' use a SQL Select command to retrieve the data from the Excel Spreadsheet
            ' the "table name" is the name of the worksheet within the spreadsheet
            ' in this case, the worksheet name is "Members" and is expressed as: [Members$]
            Dim objCommand As New OleDbCommand("SELECT * FROM [Members$]", objXConn)
            Return objCommand

        Catch ex As Exception
            MsgBox(Err.Description)
        End Try

    End Function



    Protected Sub ButtonView_Click(ByVal sender As Object, ByVal e As EventArgs) Handles ButtonView.Click

        Try
            'The ButtonView_Click event handler starts by hiding the PanelUpload and PanelImport Panels,
            ' while showing the PanelView interface (which is where the GridView is located).
            PanelUpload.Visible = False
            PanelView.Visible = True
            PanelImport.Visible = False
            'Next, a new OleDbDataAdapter object is created and its SelectCommand is assigned the OleDbCommand object returned by the ExcelConnection function.
            ' Create a new Adapter
            Dim objDataAdapter As New OleDbDataAdapter()

            ' retrieve the Select command for the Spreadsheet
            objDataAdapter.SelectCommand = ExcelConnection()
            'The purpose of this OleDbDataAdapter object is to populate a DataSet with the contents of the Excel query; this DataSet is then bound to the GridView.
            ' Create a DataSet
            Dim objDataSet As New DataSet()

            ' Populate the DataSet with the spreadsheet worksheet data
            objDataAdapter.Fill(objDataSet)

            ' Bind the data to the GridView
            GridViewExcel.DataSource = objDataSet.Tables(0).DefaultView
            GridViewExcel.DataBind()
        Catch ex As Exception

            MsgBox(Err.Description)

        End Try

    End Sub



End Class

Thanks

my pleasure