Desktop Application Will Not Allow Existing Dropbox Folder to Be Used. Error: "The folder already contains a Dropbox directory."

Thankyou Eric A & Davis A  for taking time to try to help here. I am not a beginner fortunately having been fighting with Windows since version 3 and the DX2 66 back in 1995 so at least I have the advantage of actually backing up to dataDVD everything I am not prepared to lose. It's a mixed blessing though as I can see Dropbox repeating the same mistakes as so many other software companies have since the days of IBM OS2 warp. Considering it's market penetration I am surprised to find this is program is still causing installation problems. It was about 18 years ago that windows introduced an operating system that inspected the disk structure of your PC looking for existing installations of windows. I seem to remember that also had problems at first.I think it searched for a particular marker file left by the previous installation containing an installation history and then gave you options to overwrite, create a new partition etc. It would not allow you to do anything stupid deleting, formatting or erasing things... well not after a couple of years and patches. Given the fact that dropbox is infinitely more complex in it's behavior, encryption and encoding it seems a little strange that such a fundamental point was missed unless it is some aspect of just these factors we are unaware of. Ideally when you install a new installation of dropbox on a computer it would look for a marker file in much the same way dropbox updater does and communicate between the computer and dropbox the installation history and historical & current status of the installation. It would offer intelligent choices like using the currently installed local dropbox or startng a new one on a bigger disk etc. depending on what you were doing and why. There really is only a couple of dozen reasons why anyone is reinstalling so it would not be beyond anyones ability to cater for all possibilities. logical dialog boxes to reassure the user that all is under control and then getting stuck in to reinstalling the application starting with uploading/downloading the newest additions so everything is safely backed up BEFORE checking and indexing 135,000 other files which are already safe in the cloud. Bill Gates once sent a bunch of coders to some mountain lodge somewhere with a bunch of old PC motherboards videocards soundcards and told them not to come back until they could install and update windows flawlessly... rumour has it some are still out there somewhere.

  In my own case the problem was a simple one, reinstalling XP and therefore dropbox but keeping the 220Gb dropbox I already had on drive G:\Dropbox\Dropbox where the last installation put it. Using the new advanced settings enabled me to point it to G:\Dropbox\Dropbox but after spending several hours looking at this installation and indexing files it started a new installation in G:\Dropbox and then promptly stopped as it ran out of room on the disk... announcing to me free up some room or dropbox cannot be installed... like I said Intelligent installation???. In my case I just copied G:\Dropbox\Dropbox to G:\Dropbox and after a couple of minutes and then 24hrs while dropbox indexed following with uploading the 9 important pictures it was up to date. Given that i think dropbox is a genius program especially the way it sync's between Mobile's laptops and shared & work directories this needs a bit of attention. we should not be having this discussion it needs to be press and forget flawless and instant installation with lots of reassuring noises that your stuff is safe whatever you do...