Error while activating Transfer structure

Hi All,

I have a transfer structure for Text datasource whose default Transfer Method is 'PSA'. If I activate this, it gives error:

"Error when creating transfer structure /BIC/CCBD0JOB_TEXT in source system HRDCLNT075".

The diagnosis says:

"An error occurred when creating transfer structure /BIC/CCBD0JOB_TEXT as an IDoc segment in source system HRDCLNT075".

But if I select 'IDoc' as Transfer method and activate transfer structure, it activates.

Does any one have any idea why system not allowing me to select 'PSA' and activate?

Regards,

Vikrant.