Embedded SQL generating Date/Timestamp error

I have been asked to create a program for a client that is based on one of
their existing programs that has been running in production since 1998.  I
have been given the source for their original modules, display files, etc
which I have compiled on my system without any problems.  However, when I
call the program and after working through a couple of screens one of the
modules falls over with the following error:

Program Status . . . . . . . . . . . . :   00114

             The year portion of a Date or Timestamp value is not in the
correct range (C G D F).
Previous Status  . . . . . . . . . . . :   00000

Statement in Error . . . . . . . . . . :   00001686


The module is an SQLRPGLE type and working through the compiler listing I
find that the statement causing the error is:

1686 C                   EVAL      SQL_00049  = @@DAT01F
SQL

The original SQL line, part of a cursor declaration, that uses field
@@DAT01T is:

1629 C*       l050RLSD >= :@@DAT01F and l050RLSD <= :@@DAT01T and

When I check the field usage section at the end of the compiler listing I
find that all three of the fields mentioned in the SQL statement are all
defined as 10 character dates in the ISO format, but the SQL_00049 field is
defined as 8 characters with a DMY/ format:

         @@DAT01F          D(10*ISO-)            106D   1425M   1442M   1686
         @@DAT01T          D(10*ISO-)            107D   1426M   1452M   1687
*RNF7031 L050RLSD          D(10*ISO-)             68D   1026M
         SQL_00049         D(8*DMY/)             468D   1686M

I have two questions.  First of all why would the SQL pre-compiler define
the SQL_00049 differently to the field it is supposed to represent?

Secondly, I always thought the true benefit of the date type field was that
you could move them from format to format and the system would automatically
convert them for you.  If that's not the case, why hasn't the error occurred
before on the client's system?

Thanks

Jonathan