Autonumber records inserted in gaps

[Peter Kinsman]

I have a database of about 120Mb which provides data to various front end
programs. In most tables the first field is an Autonumber primary key.
Today one of the programs showed error 3022. When I looked at the table,
eight records had been inserted in a gap left by deleted records and the
record to be added had a number that alreay existed. Other tables in the
database behavod correctly.
Compacting the database made the problem go away, but can anyone suggets
what caused it please?

Many thanks

Peter Kinsman