Please help me find my UID!!

[gmayor]

You have to tell the macro which message myItem refers to. If it is a selected item then:

Sub FindMatterNumber()
Dim strSubject As String
Dim myItem As Outlook.MailItem
    On Error Resume Next
    Select Case Outlook.Application.ActiveWindow.Class
        Case olInspector
            Set myItem = ActiveInspector.currentItem
        Case olExplorer
            Set myItem = Application.ActiveExplorer.Selection.Item(1)
    End Select
    strSubject = myItem.Subject
    MsgBox "Subject is: " & strSubject, vbInformation
lbl_Exit:
    Exit Sub
End Sub