If you’ve just upgraded from 9i to 10g, and you are using unsupported collection return types in pipelined functions you are no longer able to compile the code due to a more restrictive 10g compiler. Your pipelined functions compiled just fine on 9i. You are unable to compile the functions with the following error message PLS-00630: pipelined functions must have a supported collection return type. If rewriting huge amounts of code is not an option for you, this event will allow you to compile the code:

ALTER session SET events= '10946 trace name context level 4';