SQL & PL/SQL

Hi people,
I have create a public synonym for other users object as,

SQL> create public synonym pdep for scott.dept;


Synonym created.

then i tend to create a view on this public syn as,

SQL> create view vpdep as select * from pdep;
create view vpdep as select * from pdep
*
ERROR at line 1:
ORA-01031: insufficient privileges

I have privilege to create view.also i can create view on a public synonym of my own objects.for ex,

SQL> create public synonym cdep for dept;

Synonym created.

SQL> create view vcdep as select * from cdep;

View created.

what could be the reason behind this?is there any privilege required for me.pls suggest me.

Regards
VIDS