Implementation limit exceeded. Block size exceeds implementation restriction
This means that your SQL statement has breached the limit for SQL statement size. The limit is 64kB for statement text, 64kB for compiled BLR (see FAQ #187 to learn what BLR is) and 48kB for execution plan.
If your statement text size is under 64kB, there are some things to look for: If you use IN try converting it to EXISTS as IN gets converted to a lot of OR statements internally. If you are joining views who are UNIONs, plan could be huge and complex - try writing views that cover only those tables you really need for this particular query. If nothing helps, perhaps you can break it into several queries, or write a stored procedure to do some part of the job.
The Firebird FAQ