They have Interbase 6.0.0.627 and I use FB 1.3

Riho Ellermaa

> Is your customer running Firebird 1.0, whereas you are using
> Firebird 1.5?
>
> Being able to store NULL in an UNIQUE INDEX / CONSTRAINT is a
> new feature in Firebird 1.5.
>
> Best Regards,
> Thomas Steinmaurer