Subform no longer accepting new data

[jree3000]

I have a form that has a subform embedded within it. This form has a series of drop down boxes. Everything has been working fine for about 2 years than all of the sudden the subform will no longer allow the user to enter any data into it. Everything was working fine up to record 841. From record 842 on, the drop downs are not visible and there is no way to add data. You can still go back and manipulate data via drop down in the previous records (records 1-841) but going forward you can't do anything with the subform. I can still enter data directly in the subform's source table for all records and it will then show up in the subform but this is obviously less than ideal for my clients. Any ideas as to why this would happen or more importantly how I can rectify it?

[orange]

Readers need to know more about your tables. What do they represent? How are the tables related?
What is the purpose of the main form? the sub form? How are the forms related?

What is the business definition/process when you enter data into the subform?

[NTC]

my guess is that the cross referencing key field ; that must be common to both the main form and the sub form - is bad starting at that record. why? can't say remotely ....but that is the behavior.....