Without seeing the rowSource and rowSourceType, its hard to say. It looks like you might be manually doing some things with the combo that it is designed to automatically, and if the record pointer moves during that period of time between the ENTERS, you could have problems...

>Hi,
>Becoz the LEFT(mytable.myvalue, 3) is foreign key.
>Anyway, it works fine if user just press ENTER once but not twice. Is it curious?