I discovered a problem when using version 1.4.3 of the Git Client plugin. My Jenkins projects were working properly against a Git server using http protocol (gitlab 6). After upgrading Jenkins plugins I got version 1.4.3 of the Git Client plugin and no Git clones or pulls were possible anymore. Git clone or pull via commandline works fine. I use Git authentication via .netrc file in the home dir of the Jenkins user.

The error in the logs was:

Oct 22, 2013 10:25:52 AM org.apache.commons.httpclient.auth.AuthChallengeProcessor selectAuthScheme
INFO: basic authentication scheme selected
Oct 22, 2013 10:25:52 AM org.apache.commons.httpclient.HttpMethodDirector processWWWAuthChallenge
INFO: No credentials available for BASIC ''@git02.goertz.de:80

After downgrading to version 1.3.0 behavior was fixed again.

Version:
Jenkins 1.536
Git 1.7
Centos 6