I was trying to add a repository. The error was
Please check that the PPA name or format is correct.
It is said that this bug is with Ubuntu 13.10 which deployed in a dual-boot machine.
How can it be related? Dual-boot and adding a repository. It is very interesting.
I’m not sure if it has nothing to do with dual boot or not. The point is ubuntu 12.04 didn’t have that problem, but 13.10 has. My solution was using add-apt-repository with proxy definition. I should note that the system wide proxy settings and apt.conf proxy definitions are present. Even though they are present, I used add-apt-repository command with explicit proxy declaration.
sudo https_proxy='https://user:pass@proxy_server:proxy_port/' http_proxy='http://user:pass@proxy_server:proxy_port/' add-apt-repository ppa:webupd8team/java
Both proxy definitions should be present.