What are the possible reasons this would work in 1.5.3 but not in 2.0RC3


update invoiceheader
set paymentduedate =cast((:ptCalcDate + (:ptDays *
:ptBeforeOrAfter)) as date)
where invoiceheaderid = new.invoiceid;

it receives this message

General SQL error.attempted update of read-only column.


the statement is happening in a large procedure where many other
statements are occuring. its the only one that has a problem.

its being run as sysdba. its just a timestamp field nothing is special
about it.

What should i check for? this just started happening with 2.0RC3

Thanks