The Jenkins Version is 1.414 (2011/06/04). Why I cannot input this version into "Affects Version/s" textbox? It reports it is an invalid version...

Steps:
1. After Jenkins fresh install, I use Update Center to install MSBuilder plugin and update SubVersion plugin.
2. Because my server is sitting in an internal lan, so I configured HTTP proxy with ip and port in "Advanced" Tab.
3. When I click "install" after I tick the plugin, error reports as follows, but when I open http://updates.jenkins-ci.org/download/plugins/subversion/1.26/subversion.hpi in IE or firefox, there is a dialog showed to ask me to choose where to save the file. Why plugins cannot be installed via Update Center webpage?

java.io.FileNotFoundException: http://updates.jenkins-ci.org/download/plugins/subversion/1.26/subversion.hpi
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source)
at java.lang.reflect.Constructor.newInstance(Unknown Source)
at sun.net.www.protocol.http.HttpURLConnection$6.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at sun.net.www.protocol.http.HttpURLConnection.getChainedException(Unknown Source)
at sun.net.www.protocol.http.HttpURLConnection.getInputStream(Unknown Source)
at hudson.model.UpdateCenter$UpdateCenterConfiguration.download(UpdateCenter.java:566)
at hudson.model.UpdateCenter$DownloadJob._run(UpdateCenter.java:849)
at hudson.model.UpdateCenter$InstallationJob._run(UpdateCenter.java:957)
at hudson.model.UpdateCenter$DownloadJob.run(UpdateCenter.java:832)
at java.util.concurrent.Executors$RunnableAdapter.call(Unknown Source)
at java.util.concurrent.FutureTask$Sync.innerRun(Unknown Source)
at java.util.concurrent.FutureTask.run(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
at java.lang.Thread.run(Unknown Source)
Caused by: java.io.FileNotFoundException: http://updates.jenkins-ci.org/download/plugins/subversion/1.26/subversion.hpi
at sun.net.www.protocol.http.HttpURLConnection.getInputStream(Unknown Source)
at sun.net.www.protocol.http.HttpURLConnection.getHeaderField(Unknown Source)
at java.net.URLConnection.getHeaderFieldInt(Unknown Source)
at java.net.URLConnection.getContentLength(Unknown Source)
at hudson.model.UpdateCenter$UpdateCenterConfiguration.download(UpdateCenter.java:565)
... 9 more