> I,ve made tests for combination of simple selects, selects with joins and nested views, and every time there is limit for 128
> streams in Fb 1.5.3
>
> The same limitation - 128 - exists in FB2.0 but error info is:
> Too many Contexts of Relation/Procedure/Views. Maximum allowed is 255.

This works

select * from rdb$database, rdb$database, ... 255x

but you are right that for some constructs the limit appear to be half.
About two years ago somebody explained the reason (on devel list),
I forgot it, but I can try to find that message.

Ivan