ORA-06508: PL/SQL: could not find program unit being called tips

The Oracle docs note this on the ora-06508 error:

             ORA-06508: PL/SQL: could not find program unit being called.

Cause: An attempt was made to call a stored program that could not be found. 
The program may have been dropped or incompatibly modified, or have compiled with errors.

Action: Check that all referenced programs, including their package bodies, 
    exist and are compatible.

In Oracle warehouse builder (OWB) and other PL/SQL operations, you get the ORA-06508 error when one of the program units has not been properly compiled or it cannot be located (a problem with your $PATH environment variable).

An attempt was made to call a stored program that could not be found.  The program may have been dropped or incompatibly modified, or have compiled with errors. Check that all referenced programs, including their package bodies, exist and are compatible. 

You can run this query to find invalid objects, which may cause the ORA-06508 error:

select 
   comp_id, 
   comp_name, 
   version, 
   status, 
   namespace, 
   schema 
from 
   dba_registry;