Error with Oracle trigger, invalid identifier

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.

You should probably consider creating the Global Temp table once ... outside of this entire process ... creating it "on the fly" like this doesn't really make any sense.

Note also that the data is by default transaction based ... so those records you're inserting will tend to "dissappear" quite quickly (ie once you hit a commit).

  SQL> CREATE GLOBAL TEMPORARY TABLE temp(CID NUMBER);

  Table created.

  SQL> insert into temp ( select level from dual connect by level <= 10);

  10 rows created.

  SQL> Select * from temp;

         CID
  ----------
           1
           2
           3
           4
           5
           6
           7
           8
           9
          10

  10 rows selected.

  SQL> commit;

  Commit complete.

  SQL> Select * from temp;

  no rows selected

  SQL>

You don't need the PL/SQL block for this, and in fact creates more overhead than it's worth.