Hia All,
I even checked in debug mode and could find out these.
The table TPAKD is checked with the partner function (say SH ) and customer account group of the customer which we want as a partner function . If the match is not found then that customer will not be allowed as a SH(Ship to Party ) anywhere , even as its own partner too.
Anypne having queries could use this post as a reference. Thanks all. 