Can't open files from Dropbox even if they are downloaded to my computer

I can't open .ai files that I previously created and had stored in Dropbox. It doesn't matter wether I'm trying to open them from dropbox or I drag them to my desktop. It keeps saying, "Can't open the Illustration. The file is locked or in use." I have tried restarting my computer, loading the latest version of Illustrator, change the filed name, and checked to make sure the file isn't locked. 

I can't import .braw files into Adobe Premiere if they have been stored in Dropbox, even if they have been moved to my desktop. I've tried changing the file name as well, but keep getting a message saying that I need to download the Blackmagic extension that allows .braw files to be used. I've done that. I can work with all other .braw files unless they have been placed in dropbox. It's almost like it's corrupting them. Luckily, I still had the original .braw files that work fine. 

I'm also having the same trouble with jpg and mp4 files. Although in the case of .jpg files I've found that if I move the file to my desktop and change the file name, I can now open the file in Premiere and Photoshop.