Bug in Lookup?

V3R7M0 RPG IV

I have some variables declared for a lookup table:
D AgeDates        S               D   Dim(4) Inz(d'0001-01-01') Ascend
D InvoiceDate     S               D   Inz(d'0001-01-01')
D Per             S              3S 0 Inz(*Zero)

I have a routine that goes through these 4 dates and sets value for them, and 
in debug
they show as:

> EVAL AgeDates
  AGEDATES(1) = '2000-06-07'
  AGEDATES(2) = '2000-05-08'
  AGEDATES(3) = '2000-04-08'
  AGEDATES(4) = '2000-03-09'

INVOICEDATE = '1994-01-07'

Then I get to the call:
C                   Eval      Per = *Zero
C     InvoiceDate   Lookup    AgeDates(Per)                        9999

I get an error.

 Message ID . . . . . . :   RNX0112
 Date sent  . . . . . . :   07/07/00      Time sent  . . . . . . :   10:45:32
Message . . . . :   Date, Time or Timestamp value is not valid.

Cause . . . . . :   The Date, Time or Timestamp value is not valid. Some
  examples of values which are not valid are:
    -- A date of 1994/02/31, which is not possible.
    -- A time of 01/03:04, which does not have correct separators.
Recovery  . . . :   Correct the value of the Date, Time or Timestamp field.

What, if anything, am I doing wrong?  And if I'm not doing anythign wrong, is 
this
an RPG error?  Do I need to convert these dates to YMD numeric format instead?

Regards,

Jim Langston

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