Duplicate sources.list entry http://ftp.de.debian.org/debian/ wheezy/main amd64 Packages

My current support info shows:
================================================================================
= OS/Debian information
================================================================================
Distributor ID: debian
Description: Debian GNU/Linux 7 (wheezy)
Release: 7.8
Codename: wheezy
================================================================================
= OpenMediaVault information
================================================================================
Release: 1.19
Codename: Kralizec
================================================================================
= Date
================================================================================
Mon May 18 10:20:43 CEST 2015

but i have all the latest updates and therefore should have 1.23 of OMV-Extras.org

Question is, is that showing the correct release number? and whz am i getting the below message, whenever i do an update.

W: Duplicate sources.list entry http://ftp.de.debian.org/debian/ wheezy/main amd64 Packages (/var/lib/apt/lists/ftp.de.debian.org_debian_dists_wheezy_main_binary-amd64_Packages)
W: You may want to run apt-get update to correct these problems

no, that doesn't solve the problem.

I ran the following based on another forum I read;
/usr/bin/apt-get clean
rm -rf /var/lib/apt/lists/*
rm -f /var/cache/openmediavault/archives/*
touch /var/cache/openmediavault/archives/Packages
/usr/bin/apt-get update

Results
Duplicate sources.list entry http://ftp.de.debian.org/debian/ wheezy/main amd64 Packages (/var/lib/apt/lists/ftp.de.debian.org_debian_dists_wheezy_main_binary-amd64_Packages)
You may want to run apt-get update to correct these problems
......
W: Duplicate sources.list entry http://ftp.de.debian.org/debian/ wheezy/main amd64 Packages (/var/lib/apt/lists/ftp.de.debian.org_debian_dists_wheezy_main_binary-amd64_Packages)
W: You may want to run apt-get update to correct these problems

And per your request
cat /etc/sources.list
cat: /etc/sources.list: No such file or directory

ls -al /etc/sources.list.d/
ls: cannot access /etc/sources.list.d/: No such file or directory

solved had below entry in omv-extras-org-custom.list
deb http://ftp.de.debian.org/debian/ wheezy main contrib non-free

needed it in earlier version for some reason for the firmware of my ethernet card (if i remember correctly), guess I don't need it any more