[AccessD] Access 97 nasty behaviour of subform

good evening everyone,
I have a form with a subform,
form is continuous and has 3 little subforms in the header.
form is bound to a table.
subforms are bund to tables (which are named spaces in an EXCEL worksheet.

form has a button. when I click it, some code runs and copies and processes 
data from some other excel table to Access BE tables.

works fine so far.

at the end of the update I want to write to the one table on the excel sheet 
the project-number to indicate it has been processed.
this works as many times as I click,
but only UNTIL I close the main form and open it again.
NOW it tells me error 3027 database or object is read-only.

If I now close the main form
open the subform and change something like allow updates, THen change it 
back to what it was and save it,
THEN I can open the main form and it will happily run and update the exxel 
sheet as often as I like.

close the main form, open it again ERROR 3027.
cahnge something on subform, save, close, mainform works again for one 
opening.

I have now put me.allowedits = tru in the subform onLoad event
nochange
I have in my code tried both:
a) open the table and write to the table
b) write to the control on the subform

in both cases I get the effect that after closing the main form and 
reopening it, I get 3027 error.

any idea what I'm missing?

thank you
Lembit