Recently I got the error message, "No network connection available, operation cancelled", when I try to add a facebook sharing account. The problem is with the curl library. We need to update it the to latest version. Add extras-devel, extras-testing repository if you cannot find the library in the stable channel.
Open terminal (Ctrl + Shift + X) and give the following commands:
root #change to root user
apt-get install libcurl3
Now re-validate your facebook account from the sharing accounts.