APEX

Hello all...
I posted yesterday about a bug that I just could not figure out:

Current version of data in database has changed since user initiated update process. current row version identifier = "05FC8146C81A791FF434C18DE1E3A77A" application row version identifier = "AABB8A0C839D4636E833D7DFF4BC1162" (Row 1)

I had marked the post as answered because a key field had been marked as hidden and when I unchecked that field and declared it differently, why everything worked!

Until today! Now I am receiving the same message all over again. Is there some bug in APEX that I need to know about? Sometimes it works and sometimes it does not. I had inserted a detail line and then update two other detail lines, all in the same transacaction. When I clicked on 'Apply Changes', the updates took but the insert did not. I did not make any changes. When I tried again, now no updates take.

Has anyone heard of this problem? My SQL statement is rather complicated but I do not think the SQL is the issue. Are there switches in the APEX tool, that need to be flipped? I am at wit's end!

My SQL statement:

Select invoice_details.inv_id,
invoice_details.inv_det_id,
invoice_details.inv_type,
invoice_details.detail_comment,
invoice_details.service_begin_dt,
invoice_details.service_end_dt,
Invoice_details.name,
Invoice_details.month,
Invoice_details.year,
Invoice_details.hours,
Invoice_details.rate,
Invoice_details.inv_det_amount,
Invoice_details.expenses,
Invoice_details.wbs
From invoice_details
where invoice_details.inv_id = :P330_INV_ID
and invoice_details.wbs in (Select distinct wbs.wbs_number_id
from wbs, project
where wbs.po_number_id = :P330_PO_NUMBER
And substr(wbs.wbs_number_id,1,6) = project.wbs_sequence
And project.project_number = nvl(:F101_FPC_NUMBER,project.project_number))