You have to checkout the entire project folder in order to package.. and at least in my experience, on occasion it goes a bit stupid and you’ll have to right click the folder and choose properties and uncheck the box there that says Read-only
Perforce tries it’s best to make sure that you don’t modify/checkout something that you “can’t” and sometimes you have to just override it on the system to be editable again by unreal
So my recommendation here and what i do when i run into the “Unreal can’t write to the directory” problem is Checkout the entire Project Folder… Uncheck the box Read-Only and package… after your done all you have to do is check in the files with the PV4 app and it’ll set all the folders/files back to their appropriate read/write setting…
And then from there in the future you should be able to just do the normal work flow… That being Checkout the entire Folder, Package, Check In.. you won’t have to Uncheck the little Read-only box every time, but on occasion or something we’re doing makes it go a bit silly