On April 24, 2001, the NYISO deployed code changes affecting Class 1 PURPA
transactions in the billing system and modified bid status flagging in the
MIS.  These changes impacted settlements for 4/10, 4/11, 4/13, and 4/18 -
forward.

There was a code design problem with the PURPA code change that resulted in
an error in the computation of balancing energy for some class 1 units that
resulted in their purchasing their entire day-ahead schedules in the
balancing market.  There was also an oversight in the implementation of the
modified bid status flagging in the MIS such that those bids were not
transferred into the billing system, impacting bid production cost
guarantee settlements for the units with a modified bid status.

The NYISO will be posting supplemental invoices for April 2001 settlements
by 2300, today, Tuesday, May 15th to adjust for the aforementioned issues.
Funds due the NYISO for this supplemental invoice should be transferred
into the NYISO Clearing Account by close of business Wednesday, May 23,
2001.  Funds due Market Participants from the NYISO for this supplemental
invoice will be transferred into Market Participant accounts by close of
business Friday, May 25, 2001.

PLEASE NOTE THAT: Funds due the NYISO for the April 2001 settlements which
were invoiced on May 7, 2001 should be transferred into the NYISO Clearing
Account by close of business Wednesday, May 16, 2001, as scheduled.  Funds
due Market Participants from the NYISO for the April 2001 settlements
invoiced on May 7, 2001 will be transferred into Market Participant
accounts by close of business Monday, May 21, 2001, as scheduled.

Please be aware that as per the ISO Services Tariff any disputed amounts
are to be paid in full.  Upon resolution of the dispute, if it is
determined that an overpayment has been made by the Customer, a refund,
with interest, will be made by the ISO


In order to reconcile customer invoices for the supplemental April 2001
invoice, it will be necessary to net the following versions of the daily
advisory statements:

Date Current             Previous
1    V-2       minus          V-2
2    V-2       minus          V-2
3    V-2       minus          V-2
4    V-2       minus          V-2
5    V-2       minus          V-2
6    V-2       minus          V-2
7    V-2       minus          V-2
8    V-2       minus          V-2
9    V-2       minus          V-2
10   V-4       minus          V-3
11   V-4       minus          V-3
12   V-2       minus          V-2
13   V-4       minus          V-3
14   V-2       minus          V-2
15   V-2       minus          V-2
16   V-2       minus          V-2
17   V-2       minus          V-2
18   V-3       minus          V-2
19   V-3       minus          V-2
20   V-3       minus          V-2
21   V-3       minus          V-2
22   V-3       minus          V-2
23   V-3       minus          V-2
24   V-3       minus          V-2
25   V-3       minus          V-2
26   V-3       minus          V-2
27   V-3       minus          V-2
28   V-3       minus          V-2
29   V-3       minus          V-2
30   V-3       minus          V-2

Attached below please find banking instructions for the transfer of funds
resulting for these settlements.


(See attached file:
April_2001_Supplemental_Invoice_Banking_Instructions.PDF)
 - April_2001_Supplemental_Invoice_Banking_Instructions.PDF