hi John,
It would be nice if you could also send me your settings for thin-backup. and a list of installed plugins.
I will try to look into this problem soon.

raise the priority, because it blocks a uiser with a regular backup on a very new jenkins release.

I've tested it with 1.559 right now and it works for me on a windows 7 machine and also on a ubuntu 14.04 linux box. please add more information about the problem. Add a new log recorder with "hudson.plugins.thinbackup" and a detailed log level. add the logs to this issue.

ThinBackup config. (as you can see, I've been experimenting with the cron settings.)
This has been set like this seince the 9th. There have been no automatic backups during that interval.

<?xml version="1.0" encoding="UTF-8"?>
-<org.jvnet.hudson.plugins.thinbackup.ThinBackupPluginImpl plugin="thinBackup@1.7.4">
<fullBackupSchedule>2 * * * *</fullBackupSchedule>
<diffBackupSchedule>H 1 * * 1-5</diffBackupSchedule>
<backupPath>/var/lib/jenkins/backups</backupPath>
<nrMaxStoredFull>50</nrMaxStoredFull>
<excludedFilesRegex/>
<waitForIdle>false</waitForIdle>
<forceQuietModeTimeout>120</forceQuietModeTimeout>
<cleanupDiff>true</cleanupDiff>
<moveOldBackupsToZipFile>true</moveOldBackupsToZipFile>
<backupBuildResults>true</backupBuildResults>
<backupBuildArchive>false</backupBuildArchive>
<backupUserContents>true</backupUserContents>
<backupNextBuildNumber>true</backupNextBuildNumber>
<backupBuildsToKeepOnly>false</backupBuildsToKeepOnly>
</org.jvnet.hudson.plugins.thinbackup.ThinBackupPluginImpl>

I did create a logger with the suggested setup, and level set to ALL.
This is the last part of it. (since I saved the ThinConfig configuration changes.)

Processing request for /log/hudson.plugins.thinbackup/configSubmit
Jun 10, 2014 10:36:28 AM FINE org.kohsuke.stapler.Dispatcher
-> evaluate(<hudson.model.Hudson@1991a218> :hudson.model.Hudson,"/log/hudson.plugins.thinbackup/configSubmit")
Jun 10, 2014 10:36:28 AM FINE org.kohsuke.stapler.Dispatcher
-> evaluate(((StaplerProxy)<hudson.model.Hudson@1991a218>).getTarget(),"/log/hudson.plugins.thinbackup/configSubmit")
Jun 10, 2014 10:36:28 AM FINER hudson.security.SidACL
hasPermission(PrincipalSID:hudson.security.HudsonPrivateSecurityRealm$Details@518e0008,Permission[class hudson.model.Hudson,Read])=>null
Jun 10, 2014 10:36:28 AM FINER hudson.security.SidACL
hasPermission(GroupSID:authenticated,Permission[class hudson.model.Hudson,Read])=>null
Jun 10, 2014 10:36:28 AM FINER hudson.security.SidACL
hasPermission(EVERYONE,Permission[class hudson.model.Hudson,Read])=>true
Jun 10, 2014 10:36:28 AM FINE org.kohsuke.stapler.Dispatcher
-> evaluate(<hudson.model.Hudson@1991a218>.getLog(),"/hudson.plugins.thinbackup/configSubmit")
Jun 10, 2014 10:36:28 AM FINER hudson.security.SidACL
hasPermission(PrincipalSID:hudson.security.HudsonPrivateSecurityRealm$Details@518e0008,Permission[class hudson.model.Hudson,Administer])=>null
Jun 10, 2014 10:36:28 AM FINER hudson.security.SidACL
hasPermission(GroupSID:authenticated,Permission[class hudson.model.Hudson,Administer])=>null
Jun 10, 2014 10:36:28 AM FINER hudson.security.SidACL
hasPermission(EVERYONE,Permission[class hudson.model.Hudson,Administer])=>true
Jun 10, 2014 10:36:28 AM FINE org.kohsuke.stapler.Dispatcher
-> evaluate(<hudson.logging.LogRecorderManager@47c96519> :hudson.logging.LogRecorderManager,"/hudson.plugins.thinbackup/configSubmit")
Jun 10, 2014 10:36:28 AM FINE org.kohsuke.stapler.Dispatcher
-> evaluate(<hudson.logging.LogRecorderManager@47c96519>.getDynamic("hudson.plugins.thinbackup",...),"/configSubmit")
Jun 10, 2014 10:36:28 AM FINE org.kohsuke.stapler.Dispatcher
-> evaluate(<hudson.logging.LogRecorder@11529683> :hudson.logging.LogRecorder,"/configSubmit")
Jun 10, 2014 10:36:28 AM FINE org.kohsuke.stapler.Dispatcher
-> <hudson.logging.LogRecorder@11529683>.doConfigSubmit(...)
Jun 10, 2014 10:36:28 AM FINE org.eclipse.jetty.webapp.WebAppClassLoader
getResource(hudson/logging/LogRecorder$Target.class)=jar:file:/var/cache/jenkins/war/WEB-INF/lib/jenkins-core-1.559.jar!/hudson/logging/LogRecorder$Target.class
Jun 10, 2014 10:36:28 AM FINE org.apache.commons.beanutils.converters.StringConverter convert
Converting 'String' value 'hudson.plugins.thinbackup' to type 'String'
Jun 10, 2014 10:36:28 AM FINE org.apache.commons.beanutils.converters.StringConverter convert
Converting 'String' value 'ALL' to type 'String'
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Plugins

Ant Plugin 1.2
Credentials Plugin 1.10
CVS Plugin 2.11
Email-ext plugin 2.37.2.2
Environment Injector Plugin 1.89
External Monitor Job Type Plugin 1.2
FindBugs Plug-in 4.56
Javadoc Plugin 1.1
LDAP Plugin 1.8
Mailer Plugin 1.8
Matrix Authorization Strategy Plugin 1.1
Maven Project Plugin 2.1
Mercurial plugin 1.50
OWASP Markup Formatter Plugin 1.0
PAM Authentication plugin 1.1
SCM API Plugin 0.2
SSH Credentials Plugin 1.6.1
SSH Slaves plugin 1.6
Static Analysis Collector Plug-in 1.41
Static Code Analysis Plug-ins 1.56
Subversion Plugin 2.2
ThinBackup 1.7.4
Token Macro Plugin 1.10
Translation Assistance plugin 1.11
Warnings Plug-in 4.40
Windows Slaves Plugin 1.0

Bump. Seeing the same thing here, but not seeing anything in the logs other than "update config successful"

Nevermind. Believe it or a not, a reboot of the server seems to have corrected things

Had this issue on 2 Jenkins instances: 1.516 and 1.532.2 both using thinbackup 1.7.4

In both cases a simple restart of Jenkins resolved the issue.

reduced to minor because workaround is available and working an different systems

What's the workaround? Many Jenkins instances cannot just be restarted due to many long-running builds.

Looks related to JENKINS-16714?

This still happened to me with Jenkins ver. 2.73.3, Windows Server 2012r2.

Created a cron expression: 0 22 * * 1-5

or: H 22 * * 1-5 (as jenkins suggests to use "H"), the scheduled backup never happened. It worked only when triggered manually.

After posting this comment, I updated Jenkins to ver. 2.89.2 (there were some security updates pending, and it was recommended to update Jenkins (LTS) from 2.73.2 to 2.89.2) and now the scheduled backup works according to the cron expression.

If it is not working directly, try to restart jenkins.

may be fixed by JENKINS-28683 in in 2.129 or higher when it is available.