Can't Save Or Open Files (Folder Permissions Error But Permissions Okay...I think!)

Hello, all.

I use Dropbox from Finder and I have had this issue before (long time ago, usually no issues) but didn't know how to solve it.

I reinstalled Dropbox and restarted my MAC but still seeing the same errors: I can't seem to save a spreadsheet to a certain folder (in Dropbox but, as usual, accessed via finder) and I also can't open one that's in there. If I move the file to my Desktop I can both save and open. I see an error about permissions but I do have read and write access to the folder. I also ensured that STAFF and the EVERYONE were changed to read and write just in case, but that's not helping.

Might anyone know where I can look or what I can do? Even when I create a new folder it's happening. It seems to be a permissions thing, but I don't know what other permissions to check (nor should any NOT have the appropriate access). Not a techie here so I really appreciate the kind help from those of you who are great at this! :) THANK YOU!