Call Interface :: PRO*C Returns Non Zero In AIX 6.1 / 0 In Tru64

I am attempting to port some Pro*C code from Tru64 to AIX 6.1.I have compiled the PRO*C into an executable which is then called as follows:

host$ CJSPC004 /@WHDA 19/11/2012
Starting module : CJSPC004
Connected to the database
Running database procedure cjspk003.p_create_job_schedule
Module CJSPC004 completed successfully

However, when querying $? to get the status of the last command I get a non-zero code even though everything has worked.
host$ echo $?
39

On Tru64 this works fine with the echo $? returning a zero as expected:
host$ echo $?
0

The PRO*C was compiled using gcc