Hi,

> I am using Firebird1.03 server on Win98_se and Jaybird1.01

I would suggest to upgrade to JayBird 1.5 RC4

> Not long ago I have added a polling mechanism (about every 2 secs)
> that querys a very small table
> After adding this polling mechanism, it quite often occured, that
> the data I last wrote into the database(without any error) wasn't
> there next time

Strange. that should never happen, you should get either SQLException or
RuntimeException

> I am in autocommit mode, but still, if something is missing, it
> isn't only the last data I wrote into the db.
> Now, looking into the log file, I found the following error:
> java.lang.IllegalStateException: Can't destroy managed connection
> with active transaction
> What does this exactly mean, can this cause all of the former
> committed data to get lost?

This is most likely a bug that was fixed in JayBird 1.5. In theory what you
describe should never happen, either transaction is committed, or error
happens and it is rolled back. But the error should not dissapear.

Try upgrading to JayBird 1.5 RC4, most likely the exception will go away.
Though I cannot guarantee data will not be missed - there must be some
reason for it and I'm not sure that JayBird is the reason.

Roman