You need to grant access to the tables used by the workflow tables to the custom schema.
Thankyou for your post. Can you tell me which workflow tables? As all customize tables are stored in custom schema.
Check dba_dependencies for the package, give access for all the object. It should work.
Hope this helps.
Did you compile the package using custom schema owner in custom schema? Grant 'execute' to 'APPS' user on that package.
Most of the clients keep CUSTOM packages/Procedures/Functions/Triggers in APPS schema itself with CUSTOM naming standards (XXCUST_). Eventually all packages/Procedures/Functions need to be executed from APPS schema. follow MOS Doc 1577707.1 as mentioned by Srini
But if you want to create packages/Procedures/Functions in Custom schema, then you need to fix the dependency issue which are facing as per dba_dependencies and then provide full privilege of package to APPS schema.