Where clause query does not give correct result

I have installed freetds ( 0.82 ) on Linux machine.

I am trying to access SQLSERVER (installed on different machine) tables from
oracle ( installed on the same Linux machine ) SQLPLus editor.

Now when i execute the following SQL statement from Oracle

select table_schema,table_name
from information_schema.tables@sqlserver
where upper(table_name) not like '%_CHANGES%'

Then query returns me ???????? in the both columns.

This does not always happen. Some times it gives me correct result when i
disconnect and reconnect.

One more thing, this problem happens only when i use where clause in the
query Otherwise it works fine.

Can anybody please help me?
-- 
Thanks,
Moazzam Munir
Senior Software Engineer
Strategic Systems International