>Perhaps my problem is in an incorrect installation setting? 
>I have FB 2.5.3 on a laptop. Win 7 32 bit.
>I introduced a stored procedure and in it call F_LEFT(:varName, 24) to truncate :varName from a vc(48).
>This DB is used in Win 7 and win 8.1 else where without problem.
>
>When I run the procedure on this one box I get 
>
>ISC error 335544343
>invalidrequest BLR @offset2452
>function F_LEFT is not defined
>module name or entry point could not be found
>Error while parsing procedure myProc's BLR
>
>I reinstalled Firebird.
>I did a backup and restore of the DB. 
>No improvement.
>
>Any advice for me, beside &quo t;work smarter"?

I think this is saying that you have not installed the UDF function F_LEFT. I don't think there is any function with that name natively in Firebird (you can find it in FreeUDFLib, but then you need to install it), but I could be wrong.

Generally, I think I would recommend you to use SUBSTRING(:varName FROM 1 FOR 24) rather than F_LEFT.

HTH,
Set