> I would like to understand a couple of messages that appear in firebird.log:
>
> This is Firebird 2.1.1 CS on Debian 2.6.25.

Must note, that Debian build is different from our official build.

> 1) "page 0, page type 1 lock conversion denied (215)"
> This error is apparently related to:
> http://tracker.firebirdsql.org/browse/CORE-1970
>
> What does it mean? What causes it?
> It seems related to the header page (page 0). Is it serious (corrupts data)?

It most probably because of issue below

> 2) "Number of requested semaphores (64) is greater then size of the
> existing semaphore set (32)"
> Appeared after increasing LockSemCount from 32 to 64.
> Google was not very helpful here.
> What can be preventing the increase to the semaphore set?

Kernel must be configured (compiled ?) with more semaphores. I.e. you allow
Firebird to use 64 semaphores but OS can't allocate such amount.

Regards,
Vlad