oracle "table or view does not exist" from inside stored procedure

the scenarion is like this...

I HAVE a namespace XXX where I created some tables and some stored procedures...

THEY HAVE a namespace YYY where they created some tables...

THEY GRANTED XXX access to their tables, so when I conect to SQL Developer using XXX connection, I can do:

SELECT * FROM YYY.TableA

But if I try to run that very same statement from inside a stored procedure (either simple stored procedure or a package), the stored procedure does not compile. It happens to a lot of sp's. Is there any other permission that I have to ask for??? I'm running sp's like this:

CREATE OR REPLACE PROCEDURE PRC_SOMESP(
) AS BEGIN
END PRC_SOMESP;

Procedures that does not access YYY tables do compile well.

Thanks in advance.

After Justin Cave response, I'm trying to add "AUTHID CURRENT_USER" sentence to the sp's but getting the same "table or view does not exist" result:

CREATE OR REPLACE PROCEDURE PRC_PROC1( PARAMETERS... )  
AUTHID CURRENT_USER  
AS  
    MYVAR NUMBER;  
BEGIN  
    STATEMENTS...
END PRC_PROC1;  

CREATE OR REPLACE PACKAGE PKG_PROC2  
AUTHID CURRENT_USER  
AS  
TYPE T_CURSOR IS REF CURSOR;
PROCEDURE PRC_PROC2( PARAMETERS... )  
END PKG_PROC2  

Should I check anything else???