I've also been having this issue with Sky UI of the lag in loading the inventory as well as the papyrus ini error, and I seen to have found a solution. I'm not super technical, so don't ask me why or how this works, but after reading probably a dozon inconclusive threads like this, I did the following: Uninstalled everything (mods, Skyrim, SKSE) Reinstalled Skyrim Reinstalled SKSE Deleted the skyrim.ini and skyrimprefs.ini files that for me were located at MyDocuments/mygames/skyrim. The Papyrus settings are in the skyrim.ini file. Launched the 'SkyrimLauncher.exe' application to enable it to create new .ini files. Lanched the game using 'skse_loader.exe' I didn't get the papyrus ini error anymore and the inventory loaded as rapidly as without Sky UI. Thought I'd share. Hope it works for you.
