> In the database means as a declared object in the database. Once it is declared in the database, you can use it in both DSQL and PSQL ("stored procedure language", if you're thinking of PSQL that way).

OK, I checked, and here is how it is declared:

DECLARE EXTERNAL FUNCTION F_ADDMONTH
DATE,
INTEGER
RETURNS DATE
ENTRY_POINT 'AddMonth' MODULE_NAME 'FreeUDFLib.dll';

Does the DLL need to be in a specific location other than the UDF subfolder, or the BIN subfolder? It was already in the UDF subfolder, but I've copied it to the BIN folder as well as the database's folder, and the Firebird folder.

I've searched the web, and it seems this issue comes up quite a bit, but none of the threads I've found seem to have a definitive solution (or cause). I'm a newcomer to Firebird, and this really has me stumped (been trying to get a few simple Stored Procedures to work for days without success).