bpend_notify script design

I have bpend_notify script for solaris client.  I am setting following variable at the begining of the script.

BKUP_CLIENT=${1}

POLICY_ID=${2}

SCHED_NAME=${3}

SCHED_TYPE=${4}

BKUP_STAT=${5}

But, when the backup fails with error code  252 (no space left on target device), I am seeing BKUP_STAT variable assigned with 150. Why is it so?  Is 150 BACKUP status common for all backup failures in bpend_notify script. Can any one explain how to export accurate backup failure code into bpend_notify script for further processing ??