We've got the next error from time to time when jobs tried to update their workspace. The only solution we've found for the moment is to reboot jenkins server.

Building in workspace C:\PIC\work\jenkins-work\jobs\MyJob\workspace
Updating svn://svnserver/myproject/trunk to revision '2012-10-29T10:43:48.770 +0100'
ERROR: Failed to update svn://svnserver/myproject/trunk
org.tmatesoft.svn.core.SVNException: svn: E210003: Malformed reply from SOCKS server
at org.tmatesoft.svn.core.internal.wc.SVNErrorManager.error(SVNErrorManager.java:85)
at org.tmatesoft.svn.core.internal.wc.SVNErrorManager.error(SVNErrorManager.java:69)
at org.tmatesoft.svn.core.internal.io.svn.SVNPlainConnector.open(SVNPlainConnector.java:65)
at org.tmatesoft.svn.core.internal.io.svn.SVNConnection.open(SVNConnection.java:77)
at org.tmatesoft.svn.core.internal.io.svn.SVNRepositoryImpl.openConnection(SVNRepositoryImpl.java:1252)
at org.tmatesoft.svn.core.internal.io.svn.SVNRepositoryImpl.testConnection(SVNRepositoryImpl.java:95)
at org.tmatesoft.svn.core.io.SVNRepository.getRepositoryUUID(SVNRepository.java:280)
at org.tmatesoft.svn.core.internal.wc16.SVNBasicDelegate.createRepository(SVNBasicDelegate.java:339)
at org.tmatesoft.svn.core.internal.wc16.SVNBasicDelegate.createRepository(SVNBasicDelegate.java:328)
at org.tmatesoft.svn.core.internal.wc16.SVNUpdateClient16.update(SVNUpdateClient16.java:532)
at org.tmatesoft.svn.core.internal.wc16.SVNUpdateClient16.doUpdate(SVNUpdateClient16.java:414)
at org.tmatesoft.svn.core.internal.wc16.SVNUpdateClient16.doUpdate(SVNUpdateClient16.java:324)
at org.tmatesoft.svn.core.internal.wc2.old.SvnOldUpdate.run(SvnOldUpdate.java:27)
at org.tmatesoft.svn.core.internal.wc2.old.SvnOldUpdate.run(SvnOldUpdate.java:11)
at org.tmatesoft.svn.core.internal.wc2.SvnOperationRunner.run(SvnOperationRunner.java:20)
at org.tmatesoft.svn.core.wc2.SvnOperationFactory.run(SvnOperationFactory.java:1221)
at org.tmatesoft.svn.core.wc2.SvnOperation.run(SvnOperation.java:292)
at org.tmatesoft.svn.core.wc.SVNUpdateClient.doUpdate(SVNUpdateClient.java:315)
at org.tmatesoft.svn.core.wc.SVNUpdateClient.doUpdate(SVNUpdateClient.java:295)
at org.tmatesoft.svn.core.wc.SVNUpdateClient.doUpdate(SVNUpdateClient.java:391)
at hudson.scm.subversion.UpdateUpdater$TaskImpl.perform(UpdateUpdater.java:144)
at hudson.scm.subversion.WorkspaceUpdater$UpdateTask.delegateTo(WorkspaceUpdater.java:144)
at hudson.scm.SubversionSCM$CheckOutTask.perform(SubversionSCM.java:799)
at hudson.scm.SubversionSCM$CheckOutTask.invoke(SubversionSCM.java:780)
at hudson.scm.SubversionSCM$CheckOutTask.invoke(SubversionSCM.java:763)
at hudson.FilePath.act(FilePath.java:851)
at hudson.FilePath.act(FilePath.java:824)
at hudson.scm.SubversionSCM.checkout(SubversionSCM.java:746)
at hudson.scm.SubversionSCM.checkout(SubversionSCM.java:688)
at hudson.model.AbstractProject.checkout(AbstractProject.java:1308)
at hudson.model.AbstractBuild$AbstractBuildExecution.defaultCheckout(AbstractBuild.java:679)
at jenkins.scm.SCMCheckoutStrategy.checkout(SCMCheckoutStrategy.java:88)
at hudson.model.AbstractBuild$AbstractBuildExecution.run(AbstractBuild.java:584)
at hudson.model.Run.execute(Run.java:1516)
at hudson.model.FreeStyleBuild.run(FreeStyleBuild.java:46)
at hudson.model.ResourceController.execute(ResourceController.java:88)
at hudson.model.Executor.run(Executor.java:236)
Caused by: java.net.SocketException: Malformed reply from SOCKS server
at java.net.SocksSocketImpl.readSocksReply(SocksSocketImpl.java:128)
at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:459)
at java.net.Socket.connect(Socket.java:579)
at org.tmatesoft.svn.core.internal.util.SVNSocketFactory.connect(SVNSocketFactory.java:112)
at org.tmatesoft.svn.core.internal.util.SVNSocketFactory.createPlainSocket(SVNSocketFactory.java:68)
at org.tmatesoft.svn.core.internal.io.svn.SVNPlainConnector.open(SVNPlainConnector.java:53)
... 34 more