'mvn install' does not work & shows error while attempting to download

I am using maven 3.0.2 version.

mvn --version works fine on command line but 开发者_运维知识库when I try mvn install it does not work & shows following error.

Z:\dev\hector rantav>mvn install
[INFO] Scanning for projects...
Downloading: http://repo1.maven.org/maven2/junit/junit/3.8.2/junit-3.8.2.jar
[ERROR] The build could not read 1 project -> [Help 1]
[ERROR]
[ERROR]   The project me.prettyprint:hector:0.7.0-24-SNAPSHOT (Z:\dev\hector ran
tav\pom.xml) has 1 error
[ERROR]     Unresolveable build extension: Plugin org.apache.maven.scm:maven-scm
-manager-plexus:1.3 or one of its dependencies could not be resolved: Could not
transfer artifact junit:junit:jar:3.8.2 from/to central (http://repo1.maven.org/
maven2): Error transferring file: repo1.maven.org: Unknown host repo1.maven.org
-> [Help 2]
[ERROR]
[ERROR] To see the full stack trace of the errors, re-run Maven with the -e swit
ch.
[ERROR] Re-run Maven using the -X switch to enable full debug logging.
[ERROR]
[ERROR] For more information about the errors and possible solutions, please rea
d the following articles:
[ERROR] [Help 1] http://cwiki.apache.org/confluence/display/MAVEN/ProjectBuildin
gException
[ERROR] [Help 2] http://cwiki.apache.org/confluence/display/MAVEN/PluginResoluti
onException

Please let me how I can fix this.

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Proxy usage is a factor, hope this will help: Maven Guide to Using Proxies

If your proxy requires NTLM authentication, you'll also probably need cntlm

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The http://repo1.maven.org/maven2/ repository is down quite often, so maybe you were just out of luck that time.