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

I see the same issue. Version:
CentOS release 6.5
Jenkins ver. 1.572
ThinBackup 1.7.4

Let me know if there is more information you need.
Thanks.

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