Subject violation of FOREIGN KEY constraint
Author Rick Debay
ISC ERROR CODE:335544345
ISC ERROR MESSAGE:
lock conflict on no wait transaction
violation of FOREIGN KEY constraint "FK_RPLPO_REPLGRP" on table
"RPL_PO"

The relationship between parent and child was always valid, so I don't
know why this error was raised. Can this occur if a column in the
parent row (other than the column referred to in the foreign key) was
modified?