Thanks for your idea, DPKG
I followed your way and debugged my program, it look like this:
ENTRY:INTEGER
-------------------ROUTINE DECLERATIONS
ROUTINE ServoGun2
BEGIN
SET_VAR(ENTRY, '*SYSTEM*', '$SGSCH2[1].$THICKNESS', (intThick/ 10), STATUS)
END ServoGun2
IF intError = 0 THEN
--Read in thickness form GI[31]
GET_PORT_VAL(io_gpin,31,intThick,STATUS)
--If read GI[31] failed set error
IF STATUS <> 0 THEN
intError = 9
ENDIF
ENDIF
IF intError = 0 THEN
--Set thickness var
$SGSCH1[intPrsSch].$THICKNESS = (intThick/ 10)
ServoGun2
--CHECK FOR DRY CYCLE----
And it built successfully, thanks again for everyone.