Run-time Error '13' : Type Mismatch (1 Viewer)

Option Compare Database
Option Explicit
Private Sub Form_load()
'When the form loads the enter form will open
DoCmd.OpenForm "frmLogin"
End Sub

Private Sub cmdLogin_Click()
'The dlookup funtion allows the records to be searched within the required table
    If txtPassword.Value = DLookup("[Password]", "tblUsers", "[UserName]='" & txtUserName.Value & "'") Then
   'This is opening the main menu and then closing the form enter
   DoCmd.OpenForm "frmWelcome"
   DoCmd.Close acForm, "frmLogin"
   'txtusername.Value = Null
   'txtpassword.Value = Null
 ElseIf (txtUserName.Value) Then
    MsgBox "Enter Username and Password", vbCritical, "Error"
    txtPassword.Value = ""
    txtUserName.SetFocus
    ElseIf (txtPassword.Value) Then
    MsgBox "Enter password", vbCritical, "Error"
    txtPassword.SetFocus
 Else
   'If incorrect details are entered into any of the fields and enter is selected this would display an error message
   MsgBox "Log in details are incorrect, Please try again", vbCritical, "Error"
   'Both the fields would clear
   txtUserName.Value = Null
   txtPassword.Value = Null
   txtUserName.SetFocus

 End If
End Sub

Private Sub txtUserName_LostFocus()
    'after the user leaves the colour text box, convert the entered
    'colour to proper case, e.g. all words start with upper case letters
    txtUserName.Value = StrConv(txtUserName, vbProperCase)
End Sub

Private Sub cmdExit_Click()
 'This closes the forms down completely
 DoCmd.Quit
End Sub