Problems with composte key

I use TMS Aurelius to interface with a Legacy DB where many tables have composite keys.
In some cases both using the FIND function and using relations I get the error:
"[FireDAC][Phys][IB]invalid request BLR at offset 2911 Implementation limit exceeded block size exceeds implementation restriction."

See this example..

IdArtKey: Variant;
IdArtKey := VarArrayCreate([0,3], varVariant);
IdArtKey[0] := part1;
IdArtKey[1] := part2;
IdArtKey[2] := part3;
IdArtKey[3] := part4;
result := ObjManager.Find.Refreshing.Where(

According to Firebird FAQ:

Have you checked if it falls in any of the mentioned scenarios? It doesn't look like it's related specifically to composite keys.