I am having the exact same issue as in this question but none of the answers worked for me.

For instance, trying this answer I get this error:

a@b:~$ cd /usr/bin

a@b:/usr/bin$ sudo cp dropbox dropbox1

[sudo] password for a: 

cp: cannot stat `dropbox': No such file or directory

a@b:/usr/bin$ 

Is there a way to fix this?

Reinstalling and selecting "Start Dropbox on System Startup" worked as in darent's answer.