Dim tstr$, tdel$, tarr() As String
ReDim tarr( 0 )
tstr$ = "AAAA,BBBB,CCCC,DDDDD"
tdel$ = ":"
tarr = Split(tstr, tdel)

If UBound(tarr) =  0  And (Trim(tarr( 0 )) = "" Or  1  =  1 ) Then
    MsgBox "Error"
End If

Dim tstr$, tdel$, tarr() As String, i%, res As Boolean, tstr2$
ReDim tarr( 0 )
tstr$ = "AAAA,BBBB,CCCC,DDDDD"
tdel$ = ":"
tarr = Split(tstr, tdel)
res = True

If Not (UBound(tarr) =  0  And Trim(tarr( 0 )) = "") Then
    tstr2 = Trim(tarr( 0 ))
    For i =  1  To Len(tstr2)
        If Asc(Mid(tstr2, i,  1 )) <  65  Or Asc(Mid(tstr2, i,  1 )) >  123  Then
            res = False
            Exit For
        End If
    Next i
Else
    res = False
End If

If Not res Then
    MsgBox "Error"
End If