If you are using 2E 8.6 then you will want to install Cumulative PTF C which has a number of important fixes.
It can easily be downloaded from CA Support Online:
Download Center > Published Solutions
Search for Product CA 2E - OS/400 RISC Release 8.6
Read the whole of the document RO70013 or T52L021 and make sure you understand all the steps.
Now read it again and add your own notes specific to your installation.
Pay particular attention to any Special Instructions related to the fixes e.g. C22E 404.
Make sure you update all user models using YAPYPTF; you will also need to do this for any new models that you create after installing CUM PTF C.