Thank you for the reply but it does not answer my question. I repeat that I have opened the Relationship window and tried to make the link one-to-many and then I got the Referential integrity violation message so the question is how I can find which entry is violating the referential integrity. I thought my first message was clear. Please help

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Reply from Alex Hedley:

So you tried to set up the RI after you'd already entered some data?

Try searching for Reocrds that don't include a BookID

Something like this might work:
Without knowing the exact Table Names and Fields you will need to update accordingly:

select *
from junctionT t2
where not exists(
    select 1
    from BookT t1
    where t1.BookID = t2.BookID
)