This pertains to the basic/free version of Dropbox. Dropbox is saying I'm trying to run it on a different computer and that I've exceeded the 3 computer limit. However, that is not true. I even signed-out and closed Dropbox on the effected computer and then tried to start it again, as advised, but that does not work.
When I sign back in I'm shown the screen that follows:
Something that is probably different than most situation in this case is that I do run my computers using multi-boot. In that I have multiple instances of the same Windows operating system that I can boot. In this case it is in fact the same installation of Dropbox running on each system. I've been doing this for as long as I've been using Dropbox without any problem. While I can't say with certainty how long that has been it is probably pretty close to as long as Dropbox has existed.