Whenever I try to update plugins using the Jenkins-UI or even downloading them with Firefox I get a 404-error.
I found the following discussions relating this kind of problem to a proxy:
http://jenkins.361315.n4.nabble.com/Jenkins-site-down-td4504875.html
http://jenkins.361315.n4.nabble.com/Jenkins-download-page-seems-to-be-down-td3520292.html
Unfortunately, these discussion don't point to a reliable solution. Not using the proxy is not an option in our company.
Error-Message:
hudson.util.IOException2: Failed to download from http: at hudson.model.UpdateCenter$UpdateCenterConfiguration.download(UpdateCenter.java:659)
at hudson.model.UpdateCenter$DownloadJob._run(UpdateCenter.java:978)
at hudson.model.UpdateCenter$InstallationJob._run(UpdateCenter.java:1121)
at hudson.model.UpdateCenter$DownloadJob.run(UpdateCenter.java:957)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:441)
at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:303)
at java.util.concurrent.FutureTask.run(FutureTask.java:138)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
at java.lang.Thread.run(Thread.java:662)
Caused by: java.io.FileNotFoundException: http: at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:39)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27)
at java.lang.reflect.Constructor.newInstance(Constructor.java:513)
at sun.net.www.protocol.http.HttpURLConnection$6.run(HttpURLConnection.java:1496)
at java.security.AccessController.doPrivileged(Native Method)
at sun.net.www.protocol.http.HttpURLConnection.getChainedException(HttpURLConnection.java:1490)
at sun.net.www.protocol.http.HttpURLConnection.getInputStream(HttpURLConnection.java:1144)
at hudson.model.UpdateCenter$UpdateCenterConfiguration.download(UpdateCenter.java:629)
... 9 more
Caused by: java.io.FileNotFoundException: http: at sun.net.www.protocol.http.HttpURLConnection.getInputStream(HttpURLConnection.java:1439)
at sun.net.www.protocol.http.HttpURLConnection.getHeaderField(HttpURLConnection.java:2301)
at java.net.URLConnection.getHeaderFieldInt(URLConnection.java:579)
at java.net.URLConnection.getContentLength(URLConnection.java:474)
at hudson.model.UpdateCenter$UpdateCenterConfiguration.download(UpdateCenter.java:628)
... 9 more
Critical 
Daniel Schaarschmidt
created issue -
Daniel Schaarschmidt
made changes -
Mikko Mattila
made changes -
Jenkins IRC Bot
made changes -