Error messages from a procedure invoked by a form trigger are not displayed

I have a private POST-UPDATE trigger in form ORDERS that invokes a procedure whose task is to extract certain lines from the current order and insert them into a new order (this isn't particularly relevant). The procedure checks certain data and displays error messages if the checks fail. It transpires that these error messages are displayed when the procedure is run from a menu, but not when invoked from a form, which is when they are needed the most.

Below I describe a slightly complicated way to get around this problem. First I defined a new table TEST_ERRMSGS that has four fields: AKEY, USER, PROG and MESSAGE, where the first three fields create the composite primary key ('U' in Priority-speak). I can't be sure that someone else is going to run the same procedure, probably on a different order but who knows, so I need maximum 'separation'. AKEY will be the order number, USER is of course the user's number and PROG is the number of the procedure. Here is the relevant part of the form trigger pre-enhancement

SELECT SQL.TMPFILE INTO :ECORDERS FROM DUMMY;
LINK ORDERS OEC TO :ECORDERS;
GOTO 999 WHERE :RETVAL <= 0;
INSERT INTO ORDERS OEC
SELECT * FROM ORDERS ORIG
WHERE ORD = :$.ORD;
EXECUTE WINACTIV '-P', 'TEST_SEPARATE', 'ORDERS',
:ECORDERS;
UNLINK AND REMOVE ORDERS OEC;

Here are the lines that have to be added before the line 'EXECUTE WINACTIV'; one private integer field is utilised although this could be any field in the order as long as the procedure doesn't need it in the course of its normal execution. There's no need to worry about overwriting important data as it's a linked table that is being updated. Of course, it's best to use a private field. 

:TEST_PROG = 0;
SELECT EXEC INTO :TEST_PROG
FROM EXEC
WHERE TYPE = ‘P’
AND ENAME = 'TEST_SEPARATE'
;
SELECT SQL.TMPFILE INTO :ECORDERS FROM DUMMY;
LINK ORDERS OEC TO :ECORDERS;
GOTO 999 WHERE :RETVAL <= 0;
INSERT INTO ORDERS OEC
SELECT * FROM ORDERS ORIG
WHERE ORD = :$.ORD
;
UPDATE ORDERS OEC 
SET TEST_FIELD = -1 /* this signifies that the procedure is called from an order */
WHERE ORD = :$.ORD;

At the beginning of the procedure, the following query is executed to get the order number

LINK ORDERS TO :$.PAR;
ERRMSG 1 WHERE :RETVAL <= 0;
SELECT ORD, ORDNAME, CUST
INTO :OLDORD, :ONAME, ::CUST
FROM ORDERS WHERE ORD > 0;
UNLINK ORDERS;

To the SELECT list, I add the private field TEST_FIELD that is selected into the variable :FROMFORM. After this is the block

GOTO 10 WHERE :FROMFORM <> -1;
:TEST_PROG = 0;
SELECT EXEC INTO :TEST_PROG
FROM EXEC
WHERE TYPE = 'P'
AND ENAME = '$';
DELETE FROM TEST_ERRMSGS
WHERE USER = SQL.USER
AND AKEY = :ORD
AND PROG = :TEST_PROG;
LABEL 10;

In other words, if there is already an entry in the table for this user, order and procedure, clear it so that we can start afresh. Now the procedure runs, and every time that it detects an error, the rather cumbersome code that appears below has to be included. If before the code was

ERRMSG 62 FROM ORDERSA
WHERE ORD = :ORD
AND TEST_CONDITION = 'Y';

It now becomes

:ERR = 0;
SELECT 62 INTO :ERR
FROM ORDERSA
WHERE ORD = :OLDORD
AND TEST_CONDITION = 'Y';
GOTO 862 WHERE :ERR = 0;
GOSUB 9990;
ERRMSG 62;
LABEL 862;
...
SUB 9990;
GOTO 9991 WHERE :FROMFORM <> -1;
SELECT ENTMESSAGE ('$', 'P', :ERR) INTO :PAR1 FROM DUMMY;
INSERT INTO TEST_ERRMSGS (AKEY, USER, PROG, MESSAGE)
VALUES (:OLDORD, SQL.USER, :GLOB_PROG, :PAR1);
LABEL 9991;
RETURN;

Going back to the form trigger, after the line 'EXECUTE WINACTIV', the following has to be added

SELECT MESSAGE INTO :PAR1
FROM TEST_ERRMSGS
WHERE USER = SQL.USER
AND AKEY = :$.ORD
AND PROG = :TEST_PROG;
ERRMSG 990 WHERE :RETVAL = 1;

In other words, without digging into the code, the calling trigger has to signify to the procedure that it is being run from a trigger (TEST_FIELD = -1). The procedure then inserts a record into a special table if an error is detected, where the record includes the order number, the user, the procedure and the error message to be displayed. When the trigger resumes execution, it checks whether there is a suitable record and if so, displays the error message. This means that the record will remain in the table but this doesn't matter much for if the user runs the same procedure on the same order, the record will be deleted at the beginning of the procedure.