Just installed xubuntu 18.04 today on dell optiplex 755 (former Win 7). Everything seems to be working fine except for dropbox. Installed dropbox nautilus via "Software" and signed in at the Dropbox website. Dropbox icon in top right panel appears normally and it indicated that it was syncing and finally that syncing was complete, but I cannot open the icon to see the contents. The dropbox icon in the program menu has same problem, cannot open it. No response at all when left-clicking. Restarting the machine has not helped. When I first installed Dropbox via Software, there was a notice about the system not having installed "python-gpme" (or somesuch) and that some aspect of Dropbox might not work because of that, but in Software I couldn't find anything about the python it mentioned.