Answer
On IFSAPP10, this is an expected limitation, not a setup problem — several administration tasks under Solution Manager, including full user creation and Permission Set assignment, still require IEE on Apps10; Aurena's administration capabilities there are more limited than IEE's. In IFS Cloud's Aurena client, this same administrative functionality is available directly, without needing to fall back to IEE — this is one of several areas where Apps10 Aurena and Cloud Aurena differ in administrative completeness.