If I run the test in a once, there are some duplicate IDs (2 or 3) in 2000 records

However, if I run the test in 10 separate sections of 200 records per time,
there is no duplicate ID

(zapping the table and starting from zero)

I think it's more a matter of memory problem rather than a fail in the lock () , unlock process

What do you think ?

Both testes type performed using 3 different forms adding data to the table at the same time.