I was having the same problem but seem to have found a possible solution.
I have recently purchased a new computer running Windows 10.
I have two dropbox accounts - one for family and one private.
I setup the private account successfully in my workspace.
I wanted to setup the second account - so I created another user.
I logged in as that user but I came up with the Error 2 message.
I logged back into my account and gave that user Admin privileges but the same message appeared when I attempted to install Dropbox again.
I restarted my computer - logged into the second user account and had success installing the second Dropbox account.
Hope that helps - regards Ken
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(Windows 7) In system manager (ctrl+alt+del) I clicked show processes for all users. I stopped everything what had Dropbox in the name. Then I uninstalled Dropbox. After that I run installer again. During uninstalling old versions of Dropbox were removed. I saved 2 GB dysk space.