To check your loop, try this ...
Private Sub OK_Click()
Dim i As Integer, n As Integer
Dim Chosen As Integer
Dim CurList As ListBox
Dim UserForm As frm
'updated appl
Application.ScreenUpdating = True
'login to the system
MsgBox "Please Sign-on to ""MRUSB"" DATABASE When Promted."
STS = EssVConnect32(Null, gUsername, gPassword, "Ess02.us.bank-dns.com", "MRUSB", "Mrdata")
If STS <> 0 Then Exit Sub
'picking variables
n = 0
For i = 0 To ListBox1.ListCount - 1
n = n + 1
'defining cell location of the comboboxs
If ListBox1.Selected(i) = True Then
Worksheets("NON II").Range("F6") = ListBox1.List(i)
Worksheets("NON II").Range("F9") = ComboBox1.Text
Worksheets("NON II").Range("AE9") = ComboBox2.Text
Worksheets("NON II").Range("f7") = ComboBox4.Text
Worksheets("NON II").Range("f8") = ComboBox5.Text
Sheets("Non II").Select
'Retrieving data from the system
'RetrieveNON_II Range on NONII tab
Sheets("Non II").Select
esb_Retrieve9
'RetrieveExp Range on Exp tab
Sheets("Exp").Select
' esb_Retrieve1
'Print reports
Sheets("NON II").Select
ActiveWindow.SelectedSheets.PrintOut Copies:=1
Sheets("Exp").Select
' ActiveWindow.SelectedSheets.PrintOut Copies:=1
End If
Next i
MsgBox "You looped " & n & " number of loop(s)!", vbOKOnly + vbInformation, "Amount"
frm.Hide
Sheets("Non II").Select
End Sub
It appears your just skipping all the loops if the listbox item isn't selected. Are you sure that's what you want?