error when runing apt-get update\

[Linux for blind general discussion]

Hi folks,
How do I fix this error message?
Reading package lists... Done
W: Duplicate sources.list entry http://linux.dropbox.com/debian/ jessie/main amd64 Packages
(/var/lib/apt/lists/linux.dropbox.com_debian_dists_jessie_main_binary-amd64_Packages)
W: You may want to run apt-get update to correct these problems
There is only one entry in my sources.list for this application, so I don't know why it's growling.


Mark Peveto
Registered Linux user number 600552
Everything happens after coffee!