unrecognized data type on dblink

Hi all,
I have a problem with dblink from oracle to postgresql.

I cannot read varchar colums from postgresql db, in the trace file the
message is in the trace file is : unrecognized data type.

How can I solve this problem

Oracle version is 10.2.0.1 on windows 2003 machine and postgresql is 8.2.3
on Centos 4.4