Page Data Inconsistent with Database (18, 1) error

Hello:

We are getting this error while testing some coding changes to custom pages.  The page was originally Update/Display but now is changing to Add as well, to insert new records rather than update the existing records to the custom table.

There are 2 almost identical pages (Medical election / Dental election) w/the same grid/record on them at Level 1.  The record contains EE benefit election data - one row for each (medical plan type 10 / dental plan type 11). 

Page 1 (medical) is working fine with the new changes.  The EE can save/continue through the page and (I see a new record inserted in the table with all correct data.)  It transfers you to page 2 - if you hit save/continue, the error occurs.