System.Data.OleDb.OleDbException: 'No value given for one or more required parameters.'

[Alafujah]

Private Sub btnEdit_Click(sender As Object, e As EventArgs) Handles btnEdit.Click
Dim sql As String
User.BookingDate = CDate(dgvBookings.CurrentRow.Cells(0).Value).Date
User.Lesson = dgvBookings.CurrentRow.Cells(1).Value
User.NumberOfDevices = dgvBookings.CurrentRow.Cells(2).Value
sql = "SELECT BookingNo FROM tblBookings WHERE BookingDate = '" & CStr(User.BookingDate) & "' AND LessonNumber = '" & CStr(User.Lesson) & "' AND NumberOfDevices = '" & CStr(User.NumberOfDevices) & "' AND UserID = '" & CStr(User.UserID) & "';"
ds = Con.SqlSelect(sql)
User.BookingID = ds.Tables("Results").Rows(0).Item(0)
sql = "SELECT DeviceID FROM tblDeviceBookings WHERE BookingNo = '" & CStr(User.BookingID) & "';"
Con.Reset()
ds = Con.SqlSelect(sql)
sql = "SELECT DeviceTypeID FROM tblDevices WHERE DeviceID = '" & CStr(ds.Tables("Results").Rows(0).Item(0)) & "';"
Con.Reset()
ds = Con.SqlSelect(sql)
sql = "SELECT DeviceTypeName FROM tblDeviceType WHERE DeviceTypeID = '" & CStr(ds.Tables("Results").Rows(0).Item(0)) & "';"
Con.Reset()
ds = Con.SqlSelect(sql)
User.TypeOfDevice = CStr(ds.Tables("Results").Rows(0).Item(0))
frmBookings.Show()
End Sub

I'm trying to create a section of my system where several different values, some from a datagridview and some from an access database, are stored in the global class User where they can then be taken to another form for editing. However, whenever I try to execute the first query in this sub (using the function below), I get the error in the title of this question. I have checked that all of the required values are there at the time of execution (using breakpoints) but it still gives me this error.

Any help would be much appreciated.


Function SqlSelect(ByVal sqlString As String)
da = New OleDbDataAdapter(sqlString, Con)
da.Fill(ds, "Results")
Return ds
End Function


Example sqlString value (that causes the error):

"SELECT BookingNo FROM tblBookings WHERE BookingDate = '20/03/2019' AND LessonNumber = '2' AND NumberOfDevices = '3' AND UserID = '3';"

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