> The test server is a fresh install, Mandrake 10.1, Firebird 1.5.2,
> JBird 1.5.5

Did you use InterClient with this server, or was is different one?

> jdbc:firebirdsql://localhost/RiskAssessment.fdb?sqldialect=1

Wrong, properties are case sensitive, should be sqlDialect.

> The stack trace of the error is
>
> org.firebirdsql.jdbc.FBSQLException: GDS Exception. 335544569. Dynamic
> SQL Error
> SQL error code = -804
> Data type unknown

Frankly speaking it does not wonder me, since this is the same code as int
"WHERE ? IS NULL", server cannot guess the data type. This issue also
irritates me, but server developers say that it is not so easy to change.

What is not clear to me, why it worked before...

Roman