Anomalies in database link querying (Oracle to MS SQL Server 2005)

When i do 

SELECT 
    *
  FROM Orderdetail@"DB"

query executes in 0.561 seconds..

when i do 

SELECT 
    *
  FROM Orderdetail@"DB" where "ItemNumber" = 10242;
This query was running for 10 minutes before i canceled it, (i know we have a itemnumber 10242

when i do 
SELECT 
    *
  FROM Customers@"DB";

I get
ORA-28500: connection from ORACLE to a non-Oracle system returned this message:
[Microsoft][ODBC SQL Server Driver][SQL Server]Invalid column name 'A'. {42S22,NativeErr = 207}[Microsoft][ODBC SQL Server Driver][SQL Server]Invalid column name 'RContactName'. 
ORA-02063: preceding 2 lines from DB
28500. 00000 -  "connection from ORACLE to a non-Oracle system returned this message:"