Owncolud client on Debian squeeze

No worries at all. Did you by any chance use the download method ‘Grab binary packages directly’?
If yes, make sure to run the following before running any further commands in order to remove the broken installation:

apt-get -f install

In a debian stretch docker container I was able to install ‘owncloud-client’ version ‘2.2.4+dfsg-2’ with only the standard repositories enabled (/etc/apt/sources.list):

deb http://deb.debian.org/debian stretch main
deb http://security.debian.org/debian-security stretch/updates main
deb http://deb.debian.org/debian stretch-updates main

So you should be able to just run as root

apt-get install owncloud-client

If you need a more up to date desktop client (version 2.5.4.11654+oc-515) run the following commands (also as root):

wget -nv https://download.opensuse.org/repositories/isv:ownCloud:desktop/Debian_9.0/Release.key -O Release.key 
apt-key add - < Release.key 
echo 'deb http://download.opensuse.org/repositories/isv:/ownCloud:/desktop/Debian_9.0/ /' > /etc/apt/sources.list.d/isv:ownCloud:desktop.list 
apt-get update 
apt-get install owncloud-client

Hope that helps, let me know should you have any further questions.
Cheers,
Erik