Unknown Block Format

[s_porkalai]

Hi,
i'm getting the following error...

main_program: Ascential DataStage(tm) Enterprise Edition 7.5.2
Copyright (c) 2004, 1997-2004 Ascential Software Corporation.
All Rights Reserved
main_program: orchgeneral: loaded
main_program: APT configuration file: /Ascential/DataStage/jobdir/config.apt
main_program: This step has no datasets
main_program: Requesting delayed metadata.
main_program: This step has 10 datasets:
main_program: Fatal Error: unknown block format

Job details:
In the Job, i'm using MQ as source and Teradata Tpump as Target.
APT Settings:
$APT_LATENCY_COEFFICIENT=0
$APT_DEFAULT_TRANSPORT_BLOCK_SIZE=9800
$APT_AUTO_TRANSPORT_BLOCK_SIZE=True

While running the job i'm getting Fatal Error as 'Unknown block format'.
On changing $APT_AUTO_TRANSPORT_BLOCK_SIZE=False, then the job is getting finished without any errors. but the messages in the MQ are not getting processed immediately.
This error is not consistent for all tables. Out of 7 tables, i'm not getting this error for 2 tables when $APT_AUTO_TRANSPORT_BLOCK_SIZE=True.
How to overcome this issue without changing $APT_AUTO_TRANSPORT_BLOCK_SIZE=True?

[ray.wurlod]

I suspect that the "block" referred to is an unknown MQ message type (header?) rather than anything within DataStage.