Validating a text box

[manil]

hi! i want to make validation on a text box so that the first character is only A, B, C, or X..

sCustomerAccountNumber = txtCustomerAccountNumber.text

If sCustomerAccountNumber.Chars(0) <> Chr(65) Then
            sErrorMessage = sErrorMessage & "Customer Account Number should start with a letter!" & vbCrLf & "e.g. A, B, C or X" & vbCrLf & "e.g. A1234567" & vbCrLf
            bErrorOccurred = True
        ElseIf sCustomerAccountNumber.Chars(0) <> Chr(66) Then
            sErrorMessage = sErrorMessage & "Customer Account Number should start with a letter!" & vbCrLf & "e.g. A, B, C or X" & vbCrLf & "e.g. A1234567" & vbCrLf
            bErrorOccurred = True
        ElseIf sCustomerAccountNumber.Chars(0) <> Chr(67) Then
            sErrorMessage = sErrorMessage & "Customer Account Number should start with a letter!" & vbCrLf & "e.g. A, B, C or X" & vbCrLf & "e.g. A1234567" & vbCrLf
            bErrorOccurred = True
        ElseIf sCustomerAccountNumber.Chars(0) <> Chr(88) Then
            sErrorMessage = sErrorMessage & "Customer Account Number should start with a letter!" & vbCrLf & "e.g. A, B, C or X" & vbCrLf & "e.g. A1234567" & vbCrLf
            bErrorOccurred = True
End If

what happens with these code is whenever i try to put in A, B, C, or X.. i get the error message.. should i convert this into a loop..??