I wonder if I get the correct error message, since executing
the query in error standalone using IB_SQL by itself works fine.

IB_Monitor function mon_interprete ( buffer: PChar;
status: ppstatus_vector
): isc_status; stdcall;

uses the FB1.xx replaces _interprete, which has been replaced in FB2.0 by
fb_interpret by Valderama,
since it was overflowing according to FB2.0 documentation.