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Error: Number of query values and destination fields are not the same
Public Class RoomInfo

    Dim ValTx As String
    Dim ValNr As Integer

Private Sub cboRoomType_DropDown(sender As System.Object, e As System.EventArgs) Handles cboRoomType.DropDown
        cboRoomType.Items.Clear()
        qry = "select RoomType from tblRoomType"
        cmd = New OleDb.OleDbCommand(qry, con)
        dr = cmd.ExecuteReader

        While dr.Read
            cboRoomType.Items.Add(dr("RoomType"))
        End While
    End Sub
    Private Sub cboRoomType_SelectValueChanged(sender As Object, e As System.EventArgs) Handles cboRoomType.SelectedValueChanged
        ValTx = cboRoomType.Text
        qry = "select RoomType from tblRoomType where RoomType = '" & ValTx & "'"

        cmd = New OleDb.OleDbCommand(qry, con)
        dr = cmd.ExecuteReader

        If dr.Read Then
            ValTx = dr("RoomType")
        End If
    End Sub

    Private Sub btnNext_Click(sender As System.Object, e As System.EventArgs) Handles btnNext.Click
        qry = "Insert into tblCheckIn (Guest_ID, GRoomType, GRoomNo, GRoomID, GRoomAmount, CheckInDate, Days, ChecOutDate) values ('" &
            txtGuestID.Text & "','" &
            ValTx &
            txtRoomNo.Text & "','" &
            txtRoomId.Text & "','" &
            txtRAmount.Text & "','" &
            dtpCheckIn.Value &
            txtDays.Text & "','" &
            dtpCheckOut.Value & "')"

        cmd = New OleDb.OleDbCommand(qry, con)
        dr = cmd.ExecuteReader()

        MsgBox("Successfully added in the database")
    End Sub

I dont know what the problem is here. I guess it's the combobox, the selected value in combo box should be added in database. What is the right correct value for that combobox? Can someone help me?

The person who kindly provided this answer to your previous question showed you (1) how to use Parameter statements in your code, and (2) that when you run INSERT (or UPDATE, or DELETE) statements you do not use .ExecuteReader(). You really should make SOME effort to learn from what the nice people here are telling you.

ValTx & you need to add a comma here: ValTx & ", " &

It is telling you that you have specified a different number of column to insert into (8) than the number of values to insert (6). This is because you have concatenated 2 of the values into 2 field I believe, just count them and you will see what I mean.
