MRU checksum error on tabular form - please help - is intermittent.

Question

Good old error
"Error in mru internal routine: ORA-20001: Error in MRU: row= 1, ORA-20001: ORA-20001: Current version of data in database has changed since user initiated update process. current checksum = "84A1B18AC58C9ACF03A56DA81FD75F4A", item checksum = "557F9719C364FB3D758290FB612E5FBC"., update "HBMRX"."RX7B_NODE_ALLOC" set "NODE_ALLOC_ID" = :b1, "CALC_BASIS_ID" = :b2, "QUANTITY" = :b3, "FORMULA_FLAG" = :b4, "FORMULA_TX" = :b5"
In the past when I have had this out of the blue I usually delete the region and recreate and all is fine. However I am having this error on a region in APEX 3.0 and have recreated and is intermittent.
SQL for region is similar to:
select
"NODE_ALLOC_ID",
"NODE_ALLOC_ID" NODE_ALLOC_ID_DISPLAY,
"CALC_BASIS_ID",
"QUANTITY",
"FORMULA_FLAG",
"FORMULA_TX"
from NA
where NODE_ALLOC_ID IN
(select na.node_alloc_id
from one source
UNION
select na.node_alloc_id
from another source
Updateable columns are:
"CALC_BASIS_ID",
"QUANTITY",
"FORMULA_FLAG",
"FORMULA_TX"
I have removed all Select lists and made them text fields only. I have deleted the region and rebuilt from scratch - rebuilding the MRU and MRD processes.
Most of the time it will save fine - but on about the 5th time it will error with a checksum error.
EG - edit formula_tx - add 123 - SAVE - works
then edit formula_tx add 123456 - SAVE - errors.
This is occuring on about 5 pages where I have an identical region.
Any ideas are very welcome !!

Answer 1

Thanks for the response (handle changed)
I have had some success today with my problem in finding there is one particular column that seems to be the cause (make it non updateable and the problem goes away) - so I will try and find out the reason for this and will post back.
If I have no joy I will upload a similar scenario onto apex.com
Marc - I am only updating one table (NA) - the criteria is looking in two places to show particular nodes which meet the criteria to be displayed on screen.
select
"NODE_ALLOC_ID",
"NODE_ALLOC_ID" NODE_ALLOC_ID_DISPLAY,
"CALC_BASIS_ID",
"QUANTITY",
"FORMULA_FLAG",
"FORMULA_TX"
select
"NODE_ALLOC_ID",
"NODE_ALLOC_ID" NODE_ALLOC_ID_DISPLAY,
"CALC_BASIS_ID",
"QUANTITY",
"FORMULA_FLAG",
"FORMULA_TX"
from NA
where NODE_ALLOC_ID IN
(select na.node_alloc_id
from one source
UNION
select na.node_alloc_id
from another source
where NODE_ALLOC_ID IN
(select na.node_alloc_id
from one source
UNION
select na.node_alloc_id
from another source
)