I must modify a existing VFORM file, to add new fields in a screen or to
create new screens for example.

In any case FORMSPEC aborts during compile (in a VFAST file or not) with
this error :

**** PROGRAM ERROR #1 :
INTEGER OVERFLOW
ABORT: FORMSPEC.PUB.SYS
NM SYS   a.00ac74a0 dbg_abort_trace+$24
   CM SYS  % 230.404    SWITCH'TO'NM'+%4        SUSER1
   CM PROG %   5.25     VKADD'REC+%25           FF'KSAM

Can you help me ??