Yes, I'm aware this script hasn't been updated in years, but the problem exists in fully compatible mIRC version (6.34) as well.
"You don't have writing privileges in the NNScript directory"
Everytime that happens on startup, I need to reinstall 6.34, NNS and then update the NNS enabled mIRC to the newest and then add the compatibility fixes.
None of the updating and compatibility fixes are causing this, btw. It happens even if I use 6.34.