03.04.2013 09:13:04 org.jvnet.hudson.plugins.thinbackup.ThinBackupPeriodicWork backupNow
SCHWERWIEGEND: Cannot perform a backup. Please be sure jenkins/hudson has write privileges in the configured backup path 'C:\CIServer\Backup\'.
java.io.IOException: Source 'C:\Program Files (x86)\Jenkins\jobs\Bank Trunk\builds\lastFailedBuild' exists but is not a directory
at org.apache.commons.io.FileUtils.copyDirectory(FileUtils.java:869)
at org.apache.commons.io.FileUtils.copyDirectory(FileUtils.java:814)
at org.jvnet.hudson.plugins.thinbackup.backup.HudsonBackup.backupBuildFiles(HudsonBackup.java:302)
at org.jvnet.hudson.plugins.thinbackup.backup.HudsonBackup.backupBuildsFor(HudsonBackup.java:270)
at org.jvnet.hudson.plugins.thinbackup.backup.HudsonBackup.backupJob(HudsonBackup.java:208)
at org.jvnet.hudson.plugins.thinbackup.backup.HudsonBackup.backupJobsDirectory(HudsonBackup.java:196)
at org.jvnet.hudson.plugins.thinbackup.backup.HudsonBackup.backupJobs(HudsonBackup.java:175)
at org.jvnet.hudson.plugins.thinbackup.backup.HudsonBackup.backup(HudsonBackup.java:142)
at org.jvnet.hudson.plugins.thinbackup.ThinBackupPeriodicWork.backupNow(ThinBackupPeriodicWork.java:87)
at org.jvnet.hudson.plugins.thinbackup.ThinBackupMgmtLink$1.execute(ThinBackupMgmtLink.java:76)
at org.jvnet.hudson.plugins.thinbackup.hudson.model.AsyncPeriodicWork$1.run(AsyncPeriodicWork.java:54)
at java.lang.Thread.run(Unknown Source)

03.04.2013 09:12:40 org.jvnet.hudson.plugins.thinbackup.backup.HudsonBackup backupJobsDirectory
INFO: Found 63 jobs to back up.

03.04.2013 09:12:40 org.jvnet.hudson.plugins.thinbackup.ThinBackupMgmtLink doBackupManual
INFO: Starting manual backup.

Indeed, lastFailedBuild is a normal file and not a directory. Since Jenkins 1.507 there are these special files (see http://jenkins-ci.org/changelog). Do you think you can address this issue quickly?