Hi Drew,
Welcome to Box Community and glad to help!
Can we confirm your permission to the file/folder you're working on?
We'd love to further assist!
Sure, you have my permission to examine any of the files and folder in my account.
As an example, I just uploaded a simple 3-line text document at the top level ("All Files") named "test.txt". When I'm on my laptop, I can open the file in Notepad directly by right-clicking it and getting the menu that has "Open In Notepad" as the first entry. When I try the same thing on my desktop, the right-click menu doesn't have "Open In Notepad" as a choice. This is the same for every file in my account: things work as they always have on my laptop, but I can't edit any of them on my desktop. As I mentioned in my original post, this behavior just started 2 weeks ago. Before that, I've been using my Box account for years the way it used to work.
