How to reference a table from another schema inside a package?
From section "6 Coding PL/SQL Subprograms and Packages" in the "Oracle Database Advanced Application Developer's Guide, 11g Release 2 (11.2), E41502-05"


  To create without errors (to compile the subprogram or package successfully) requires these additional privileges:
  - The owner of the subprogram or package must be explicitly granted the necessary object privileges for all objects referenced within the body of the code.
  - The owner cannot obtain required privileges through roles.


You must have granted select permission on this table to the schema that owns the package. 
It is important that this permissions are granted directly to the package owner and not 
indirect using a role. Using a role is sufficient to select the table directly by Toad 
but it is not sufficient if you want to select the table in a package.